Obviously, this is about the recently announced factoid that the PS4 will not be backwards compatible with PS3 game discs. A lot of people are crying foul, but they don't really understand why. The reason is purely technological. The PS3 contained a powerful computer chip called The Cell.

No, not that Cell. It's a computer chip, not a movie. Stay with me, thanks. So, the new powerhouse of the PS4 is the QWX64KP12.-742WTFKTHXBAI. Extremely powerful chip with a completely different architecture than Jeniffer Lopez... I mean, the Cell. So, unfortunately, the PS4 simply isn't wired to play PS3 games, even though it's far more powerful. This would explain why Sony is trying to stream them to the PS4 instead. If PS3 games are being processed on Sony's servers, then all they need to do is stream them to you, and the PS4 can handle the rest. It's a clever alternative, but not really a desirable one. Not everyone has high speed internet, and some people have data caps. For those unfortunate SOUUUUUUUUUUUUUULS... *ahem* ... they're going to be hit hard when they try to stream PS3 games.
Now, let's address a common statement that I've been seeing in these discussions.
"LIKE ZOMG JUST KEEP J00 PS3 PWOBLM SOLVED N00B!"
Except, there are still problems. Let's try to understand first why some people are disapointed that there's no BC. Sony was the first company that made a backwards compatible gaming machine (technically, it was Nintendo since you could play regular Game Boy games on a Game Boy Color, but I can't really count that as the GBC wasn't entirely a new machine). The PS2 was able to play PS1 games, and it continued to play PS1 games throughout its life cycle. This set an expectation and other companies followed suit. Nintendo's Game Boy Advance was fully backwards compatible with GB and GBC games, the DS could play GBA games and the 3DS could play DS games. When the Nintendo Wii came out, it could play GameCube games, and the Wii U could play Wii games. The 360 even played old Xbox games, but that was a hot mess as they had to do it through software emulation and ceased support on that less than a year after its release. Surprise, surprise. You now started seeing Xbox games available for download...
Sony upheld the tradition of backwards compatiblity with their first generation of PS3s, not only allowing you to play PS2 games, but most PS1 titles as well. In essence, the PS3 launched with the largest library of games in console history as it supported not one but two other systems' entire libraries. That is great for a gamer's first foray with a company's system. Unfortunately, Sony was hemorraging money from the PS3 just being too bloody (I c wut I did thar) expensive, so they started scaling things down with the following generations of PS3s. Sadly, the Emotion Engine (PS2 graphics chip) had to go, but at least Sony tried to keep PS2 BC with emulation support. That didn't last long, and eventually the new PS3s were relegated to nothing more than machines that only played PS3 games. Sony started BC, and have now swiftly ended it.

Sony has limited the size of their PlayStation library now. Yes, Sony states that they will include PS1 and PS2 titles along with the PS3 titles for their cloud gaming service, but this comes at the expense of manhours, resources and money to get those title available, not to mention the service will most assuredly not be free. Want that rare niche PS1 title that no one's heard of? I doubt Sony will make that available digitally. You'll have to go to eBay or wherabouts to acquire it. Prepare to buy a PS1 or PS2 to go with it, or pull out your old console and dust it off.
"That means I got to hook up another console to my TV!"

Yeah, I know. It sounds lazy, but having another console out means having to make space. It means snaking more cords through entertainment centers. It means pulling out controllers with cords, and means more tripping hazards. The convenience afforded to us thanks to Sony and BC meant that we could retire our systems and save space. It meant that our old systems that served us well could finally be put to rest, no longer counting the days when the CD/DVD motor or lense would finally crap out. PS4 being BC with PS3 also would have meant a lot to owners of 20 and 60 gig PS3s, again because they could retire their original PS3s before the inevitable Yellow Light of Death (I got mine last year in September. R.I.P.) and if they've been playing them hard, they've put more than six years of wear and tear on them. Also, if the PS4 was BC, it would mean a lot of PS3 owners could trade in their machines towards the PS4, making it more affordable for them, thus selling more PS4s.
True, the PS4 is technically incapable of playing older games. True, we could just keep our old systems lying around. True, we buy new machines to play new games. It seems silly that some would be upset over an incovenience of having to buy an older machine or hooking up another machine to a TV to play older games, yet it was Sony who introduced us to that convenience for us in the first place. That's why seeing people bothered by no BC. They'll buy those PS4s for PS4 games, but they have every right to be disappointed. It's hard not seeing such a terrific feature that's been with the PlayStation for two generations suddenly disappear. I guess we're all just going to have to settle paying for a streaming service with a limited selection, provided our internet is fast enough and we haven't hit our data caps yet...