Because being mad at google for not providing updates is a falsehood. If you're going to be pissed, be pissed at the carriers. If you're tech savvy enough to be keeping and eye on android updates and wanting the new roms, you probably already know that it's the carrier's fault. If not, you're probably not all that mindful of when new android features are released anyway, I would say.
Apple actually supports its old devices decently well. Yeah they may be dropping a lot of features from iOS6 for the iPhone 4, but by the time that drops, the iPhone 4 will be getting closer to 3 years old, and you're almost surely past your upgrade date anyway.