Well tripod did more or less the same 5 years earlier, and had a million copycat sites. What exactly was the great idea that myspace had?
If you read up on myspace history and how they came to dominate the market it is quite obvious that it was by pushing their product relentlessly - not by innovating or having excellent ideas.
That's easy to say, but sometimes, ideas do matter.
You always have to convince someone of your idea. If you are working at a startup, you have to convince the customer/user that it's worth the time/money. These rules still apply.
An idea is like a multiplier. In itself it is worth nothing, but if someone with good execution skill can make 1 mill. $ on an idea, and your idea is twice as good (however you define that) then the same guy can make 2 mill. $ going after that idea instead, all other things being equal.
Note though that an idea that is "twice as good is hard to come by, and even harder to sell to the guy that has to execute it - if it isn't yourself.
A lot of companies (amazon for example) have made into the big league without having an idea that is in any way novel but by having great execution skill. The opposite is never the case.
I would suggest that Amazon's great execution is actually the result of continuous experimentation and the accumulation of many thousands of "small ideas." The evolution of their website is famously driven by continuous A/B testing. And I think the S3/EC2 combo may evolve into something quite novel.
