The pure RDBMS layers of Oracle and MSSQL offer mainly a more mature programmable environment than MySQL and InnoDB. T-SQL and PL/SQL can't be yet matched by MySQL stored procedures and triggers.
The other differences are syntactic and slight semantic differences which make things easier or harder (like top 500 versus limit/offset).
But the real killer is that there are a ton of integrated tools and services on top of the RDBMS layers of MSSQL (Reporting Services, Analysis Services) and Oracle (Data Warehousing, RAC) which MySQL doesn't have (yet).
