Yes, and walk into any gunshop and try to find one of these rifles you mentioned in 6.5x55. Odds are they'll give you the deer in the headlight look when you ask. Just because the chambering is listed on a website doesn't mean it's readily available. Ruger has a horrible reputation for listing rifles in calibers it's never built. I'm a gun dealer and I haven't seen a M70 featherweight in that caliber built for years, but they still list it. About every three years winchester will make a run of 100 or so rifles and that's it until they decide to tool up a few years later. Then you've still got the problem of the underloaded factory ammo that's hard to find also.

I stand by my statement that the .260 is a lot more readily available.