MySQL is more likely to have database corruption issues, and it doesn't fix them automatically when they happen. I've worked with MSSQL since version 6.5 and don't remember a database corruption issue taking the database offline. The few times I've worked with MySQL in a production environment, a database corruption issue took the entire database offline until we ran the magic "please fix my corrupted index" thing from the commandline.
MSSQL's transaction and journaling system, in my experience, handles just about anything - including a power cycle or hardware failure - without database corruption, and if something gets messed up it fixes it automatically.
This has been my experience, and I'd be happy to hear that this has been fixed or we were doing something wrong.
http://dev.mysql.com/doc/refman/6.0/en/corrupted-myisam-tables.html
http://www.google.com/search?q=site%3Abugs.mysql.com+index+corruption