On a level playing field such as linux, SQL Server would win its share against Oracle and DB/2. It is not without features, and there are people who like it.
It's just that if I've got 10,000 servers and I'm looking at a half-million dollars in Windows licenses just to use SQL Server, I might conclude that Oracle on linux was plenty good. The truth is, all those high-end databases have more features than anybody needs, and whoever is winning the benchmarks this week will be losing them next week. It's a fairly vigorous competition.