I remember near the launch of 3e there was a discussion by the designers that mentioned several points that had figured into their design of the xp scales.
1. Their research suggested that on average campaigns lasted for a certain period of time (I forget what period) and with x number of games a month.
2. They wanted to allow PC's to advance their characters through all 20 levels in the lifespan of a campaign (the older xp charts made it almost impossible to gain levels much after 12th/13th and it was rare to get to use the high level powers)
i.e. they wanted to design it in such a way that 'by the book' a campaign could take a party from 1st to 20th level within the average lifespan of a campaign.
As a personal view I think the standard rate seems too quick, mostly because there is nothing to stop it all happening in too short an elapsed time - one spring you're a wet-nosed apprentice who can't get a drink in a bar, before winter you're tossing delayed blast fireballs into said establishment!
Please excuse the hyperbole to make my point

From the point of view of a DM the party (by straight DMG) don't spend long enough at a given level to allow political events and grand schemes to move on appropriately. Another problem is that since the next level is so frequently within reach, it can make PC's have a more "experience grabbing" mentality sometimes.
Having said that, it is nice as a player to get to the higher levels in a reasonable amount of time, especially with less playing time available nowadays, so I concede that one of the designers original goals really was a sound one!
Cheers