MySQL didn't offer the richer programming environment that Oracle and MSSQL offered, especially in early incarnations, when it didn't even have Stored Procedures.
From my perspective I tend to put most of my business logic into the application, via DAO's or ORM mappers etc. Therefore the database engine underneath is less important and in theory the application is transportable.
From a management perspective MSSQL offers a number of benefits (many already listed) that make the task of owning the database a lot easier.
Microsoft also provide the excellent and lightweight SQLExpress for development, which I have found easy to work with and it integrates into Visual Studio nicely.
