The reason all youtube content is not available is the iPhone requires a fairly new video format (h.264 or some such). Most youtube content is not available in that format, yet. New stuff is being added and some old stuff is being converted every day.
RE the You tube video choices :
Do ya think it just might be that ATT might have a 'lock' on certain ones , especially large , bandwidth time consuming ones to keep we iPhoners from 'hogging' the Edge airwaves to make sure the 'big money accounts, ie the Blackberry toting lawyers, senators, doctors , brokers, etc. etc don't get peed?!?!
I've noticed too that during late at night and weekend sat./sun. etc. times that my signal strength 'bars ' where I'm at goes down 2-3 bars compared to a weekday during businesss hours. I can only think the reason is that they may be turning off/shutting down towers to save money. I get the full bar amount during the weekday from exactly the the same spot ! hmm..m.mm. !?