Firstly and most importantly, Thanks to rebase I'm constantly working against the most recent mainline, merge pains are reduced by frequently dealing with smaller rebase merges instead of trying to do one massive merge at the end when I'm finished with a longer life task that might last a week or two. The more often you merge the less painful it is.
Secondly there's the cleaning part of history involving squashing. I believe the issue with your viewing the merge history of the main line will miss out on changes that were able to be introduced fastforward without a merge. And frankly no one else on the team cares that I committed 6 times in the process of one task, they want to see all the code relevant to that task, and ideally it's all in one change set.
There's a pretty reasonable summary over here http://blog.sourcetreeapp.com/2012/08/21/merge-or-rebase/
For certain teams rebase just makes a lot of sense.