ABLITY, sure it is the factor , I agree 100%, Sometimes you have lets say 10skills you acquired through time , and a particular Client requires may be 2 or 3 of them.

In my previous company I was working as DBA / Developer , SSIS and lots of SSRS.

and the one before all client needed was SSIS and TSQL, my current position requires all TSQL 99% , no tools.

I like what I do , but don't get me wrong I want to make more money while the time is right:) . that's why move to different technology that can pay more with one or two skills in the area ( especially related to ERP, SAP , Oracle Peoplsoft , JAVA...) I thought could be a way to go. that's my observation.

the other thing is the skills that you developed in using tools both on Native sql and Third party tools ( Development or Administration ) could fade away through time.