I think it ultimately doesn't matter whether you award XP to absent players or not, provided that the players are on board.
My newbie group is has several people I work with. Unfortunately, their jobs require them to travel to clients somewhat regularly, and we have clients all over the continental U.S. and a few outside it. As such, it would be unreasonable for me to expect them to attend every session. Since it's essentially luck of the draw, I don't want them to fall behind just because they had to work. Therefore, we just assume that they were off having adventures of their own during this time. As it is, unless the group is feeling unusually generous, they still miss out on treasure.
With my other group, we've gone back and forth. Some campaigns players only earn XP if they are present, other times we just go with group XP. It works fine both ways. The latter is slightly easier however, since only one player needs to track XP (though typically at least two of them do it anyway).
One thing I've considered doing is requiring absent players to tell me what adventure their character had while they were away from the group. I've never tried it, but I kind of like the idea since it would give me additional threads to weave into the campaign.
