It needs to be pointed out that in the last 15 years, just about every major console has launched in the 2nd half of the year, with Thanksgiving week being the most popular. Christmas is HUGE. I think console launches earlier in the year always turn into flops (see 3DS for a recent example) as games are never ready.
As for an announcement 1.5 years early, I think this generation of consoles has gone one the longest ever, and trying to contain leaks just becomes impossible at a certain point, especially when dev cycles are getting longer and longer. Much like announcing the original iPhone 6 months before release, Microsoft and Sony want to be the ones controlling the message, not some random blog that may not be factually correct.
As for an announcement 1.5 years early, I think this generation of consoles has gone one the longest ever, and trying to contain leaks just becomes impossible at a certain point, especially when dev cycles are getting longer and longer. Much like announcing the original iPhone 6 months before release, Microsoft and Sony want to be the ones controlling the message, not some random blog that may not be factually correct.