I've got my 401k through Fidelity and I have consolidated my other accounts there as well. I do have the option to invest in Spartan index funds (at least the total stock market index) in my 401k and with the Spartan series available for my IRAs and such, there's no reason to move my stuff to Vanguard, since I'm paying roughly the same as I would at Vanguard for better service and tools. Fid rolled out the Spartan series a while back as a loss leader - to get you in the door and to compete with the low cost index funds available from places like Vanguard, but they hope you'll also start sampling the more expensive funds as well. But you don't have to do that.
Don't get me wrong, Vanguard is an awesome company, but you can do just as good at Fid, and they do have superior customer service and user interface/website tools. So look into the Spartan series stuff, ask at your work about adding it to your 401K (if it isn't in there already) and don't worry about it. ;)