Actually, the original artist can f*ck all he/she/they want with their own work of art!
The great Jimi Hendrix was famous for really reworking his songs in concert. His general view was that they were his songs and he wished to advance them. I feel this is completely true.
U2 have said - even when "Pop" was released - that they weren't quite done with this album. This sentiment has only grown in the years since, especially given the album's comparatively poor reception in some areas (like the U.S.). I feel revisiting songs on that album is more than justified.
Furthermore, I feel that reworking many songs, whether it's a token change of a line (like on "Mysterious Ways") or a completely new mix (as with "Numb") is a great idea - especially for a "Best Of"! If U2 re-released "Pop", perhaps your comment would be justified to some extent. However, on a "Best Of", why not remix songs a bit, try to either add a bit extra or make the songs better? Why create an album full of songs that can easily be found on the regular releases? IMO, the main disc of the 90's "Best Of" is fantastic and is oceans better than the main disc of the 80's "Best Of", which not only over-emphasized R&H, but butchered some songs (like "Streets") and failed to showcase songs from several albums (like "October"). Of course, what makes the 80's "Best Of" shine is the b-side disc, which puts to shame the horrendous 90's b-side disc.
In any event, I feel the version of "Gone" on the "Best Of" is far better. It simulates the concert feel of the song more, has better vocals (both main and back-up) and has more energy. I applaud U2 for doing this.
I'm not sure about the extended ending in "Staring at the Sun" - I don't think that does much for the song at all. But again, it is fun to hear a different mix, rather than just listen to the straight-forward "Pop" songs.
*Goes off to write a letter to Bono to tell him how he should be writing songs* 
