So you're saying that being first when win 7 and dx11 came out in september 2009 did nothing to help AMD? Really? I didn't say "being first gives you an advantage forever more and the competition can't recover", did I? Let's look at some recent examples:
gtx 480 vs 5870: 5870 shipped 7 mos earlier, AMD graphics division made record profits. GTX 480 came out VERY late/slow/hot, sales sucked.
gtx 580 vs 6970: gtx 580 was first (surprising many amd fanboys), it fixed the issues with gtx 480 plus was 15-20% faster. 6970 wasn't an epic fail, but it certainly was disappointing. And remember that it was only a month or so later, so it wasn't THAT late really.
8800gtx vs 2970: 8800gtx was the best thing since 9800 pro. Probably the best overall card nvidia has ever had. Obliterated everything in its path. 2970 was 6 mos later and it sucked: used same/more power as 8800gtx but was barely faster than 8800gts 640.
Bulldozer vs nehalem/westmere/sb: BD is the poster child for this, even worse than barcelona. EPIC FAIL. If it had come out 18 mos earlier it still wouldn't have been great, but it wouldn't have sucked nearly as much, either.
Face it, the longer the delay, the more pressure there is to really WOW your customers. Being first has consistently been a huge advantage, especially if you are so far ahead that the competition has nothing but wooden screws/hype to combat it with. Being first by a small amount (say a month or so) is still usually an advantage, but that is just a general rule and not necessarily impossible to overcome for the competition in that generation.
edit: and remember that gtx 460 was really the start of the improvements for nvidia. I don't want to get all melodramatic and say that it saved the company or anything, but up until that point AMD dominated dx 11 sales.