[Elmo]

Curosity killed the cat but I have a question. If one feels a uv filter degrades an image sometimes why does it not do so the other times?

The UV filter was ok in the old film days because the film was matt surfaced and reflected very little light back toward the lens. A digital sensor on the other hand is shinny (look at it) it reflects lots of light back into the lens causing additional flair. A lens is designed to handle some flair in its design. A filter is perfectly flat, and even with multi=coating it reflects back causing soft/fogged images.

If UV filters are so important why are filter threads omitted on all upper end long telephotos?

I only us a protective filter when conditions demand it (Rain and such). Whether one uses a protective filter is the users decision. The user must weigh the facts concerning his usage. I prefer to not use one for image quality concerns.