As a followup to my post above about ATi doing everything at once, say they had a few glitches with one of the things they are developing they either have to move resources to it or let it delay.
They are doing the r520 for themselves but they are doing the r500 for a customer, Microsoft, so it is not therefore surprising that if something would be delayed it would be their own product rather than upsetting a big customer with potentially new business in the future if this product is successful.
To put it bluntly, if Xbox R500 had a problem then you move resuroces from R520, if R520 has a problem you just extend your graphs a bit and put on a smile.
If I was in charge that's certainly what I be doing, Microsft have probably been geared up for a launch around E3 for a long time now, so any bumps after that plan from ATi's area of expertise, would need to be fixed as a priority to make sure that happened. Certainly it is not as if their current line-up, as mentioned by other posters, is struggling to sell.
I think people are being unfairly harsh on ATi, I would say the most that can be levelled at them is that maybe doing all that they are was simply too ambitious IF there is a long delay. It's not as if they have made any promises to the general public. nvidia seem to be in no hurry to ship G70 either, maybe for very similar reasons to ATi.
But seriously, for every person that walks into a BestBuy understanding that the XL is a steal, there's another sucker who's gonna see SM3.0 on the box and say "ooooh this must be worth the $50 since it's more advanced!!". 
