Actually, SQL Server is more powerful than you think. You're making it seem like it's Access. SQL Server is meant to handle millions of records, and uses a large array of features such as indexing. (MySQL comes no where near to SQL Server.) Also, one of the main reasons why companies use ASP is because they have a WindowsNT server running. They have that because it's easier to maintain and setup (the network) with Windows than it is with Linux/Unix. And since ASP comes free with WindowsNT/2K, then they go for ASP.
Sometimes just because it's a good product, doesn't mean it's efficient for the company. I think it will be a while before PHP really catches up in the community. It's certainly a hot product right now, PHP, but it doesn't come close to the number of sites running ASP.
I used to be a big ASP fan. Then I went to PHP. I loved it. Then I stepped aside and now I'm doing ColdFusion. I think ColdFusion is the most enjoyable to work with because you can do an entire application in 1/4 the time it would take with any other language.