I think this is a huge part of the issue. I have worked professionally on the big three commercial rdbms (DB2 distributed - not mainframe -, SQL Server, and Oracle). I consider myself a SQL hacker with some DBA experience and knowledge, mainly around DB design and performance tuning.
I simply don't care what rdbms I coding to, I can tweak to leverage quirkiness in T-SQL or PL/SQL if needed or advantageous to a project. And, <whispering>, PL/pgSQL.
A common experience for me when job searching is to apply for a job where, for example, they are primarily looking for Oracle PL/SQL development. I've been doing SQL coding for roughly 8 years, the last 2 years or so have been primarily in Oracle PL/SQL. I have been turned down for interviews with feedback that says "oh, we need someone with 5 years of Oracle development work."
If it's techies doing the resume reviews, I always get at least an interview. Sometimes even then, I have to sell the fact that SQL skills transfer nicely between rdbms harder than I should.
