OK, so I'm all for having a fave cartridge esp if it's one that's a bit different and ammo is not found at Wal-Mart or CDN Tire. My fave is the 257Roberts. Big deal! Who cares what I like?

Saying that, after reading the proceeding sickening 6.5x55 love fest, I still don't think there anything more magical about it than any other std cartridge of similar velocity with std C&C bullets fired in similar rifles. Wondering aloud what can it do that a .260, 7/08, 7x57, 270, 280, 308, 30/06, 303, 8x57 can't do? Do tell!
Your premise is flawed. A love for the 6.5x55 (or, if you prefer, .264 caliber cartridges in general) doesn't mean that you dislike or hold disdain for others. I imagine many 6.5x55 shooters also shoot (and enjoy!) other cartridges. I certainly do.
After all, you've indicated that you have a fave in the .257 Roberts. Nothing wrong with that. Certainly not "sickening" (odd choice of words, perhaps an attempt at whimsy?).

And I'm guessing that your appreciation for the .257 isn't exclusive.
If I had to sum it up, I like the 6.5x55 (or .264) because:
- it has a long and interesting history
- it offers a variety of bullet weights (ca. 95 gr all the way to 160 gr)
- it is suitable for a wide variety of game
- has plenty of "natural" accuracy
- offers superb ballistic co-efficient
- easy to reload, including a wide variety of components
- easy recoiling so it makes for a great choice for new shooters, smaller or female shooters, and from the bench
- offers good availability in both factory ammunition and rifle choices.
There is some overlap, obviously, and I am probably forgetting a few.
This is not to say that the 6.5x55 isn't the only cartridge to offer many or all of these things. But it stands out, imho.