The reason we did our first 2 tours with Trek Travel was exactly the reason you stated. They had the exact bike I was riding at the time. I am not good with changes in mechanical things, so it was fine. But... we rode over lots of cobbles on road bikes, as well as rain in the Czech Republic and Austria. No one seemed to care, except me. Some people did rent the hybrids.
When we went to Quebec, we took our own bikes, since we drove. This year, we absolutely loved our tour company in Spain (Cycling Country), as they are a small, husband and wife owned business. But the 48 cm Orbea sucked for me. It had the same geometry as my bike as far as stand over, top tube, etc, but I couldn't reach the brakes from the drops. For someone who doesn't like descents to begin with, it was pretty miserable. We want to do their Portugal tour in 2012, but if they don't have a wsd bike with short reach levers, we will bring our own bikes. We are thinking of getting steel bikes with s and s couplers, for travel. It would be a second bike for us (or third) and would also be used at home, too.
VBT has good tours; I know someone who works for them, who has helped us lead our AMC New Members ride. But, their bikes stopped me from considering them. We are doing a tour of the Finger Lakes in NY this year, so we can have our own bikes. It's the same company that ran our Quebec tour and they are very low key. I wouldn't use them if I couldn't have my own bike, as they provide really low end Treks.