I HAVE PLAYED IN GAMES WERE THE gm...DAMN CAPLOCKS...were the GM levels all PC's at the same time. I can live with this, but is is a measure contrary to the traditional nature of story telling. The world is diverse and someone is always better (i.e. higher level).
I hear what you're saying but that does work for us.
With everyone leveling at the same time, the group is slightly more balanced overall. Yes, you can make an argument vs Pure Casters vs Fighters and many other balance issues discussed over the years pertaining to level differences, but it's better than it was. No more kill steals for them, so they work together a bit more. No more tracking xp for me!
Everyone can get into character better and contribute to the story, but not everyone can contribute in the same way. You're right, "someone is always better" at something but it doesn't require a level difference. Whether or not it's completely
fair is open for debate. I do believe my players feel as if they are treated fairly, which is good.
I did have to do some HR tweaking.. who doesn't.
For my campaigns, Ranks in skill are more important than level. Ranks are decided by PC's and everyone get's the same DP. Your games may vary.
http://www.shamusyoung.com/twentysidedtale/?p=612
To see how a campaign you describe might really be played out, see the above.