Rich Eisen scooped this a few weeks back on Chris Russo's show on Sirius. He knew it was coming and supposedly got into some hot water for spilling the beans because I guess he was told off the record or something. And the reasoning is just like Larry says, to stretch out the calendar and squeeze another month of draft talk/build out of the media.
Eisen's other nugget that he said was coming, was a uniform "NFL Training Camp Opening Day", with all 32 team and all players reporting to camp on the same day across the league. No more staggered camp openings, rookies coming in early, etc. This will be pushed as a big event, much like the draft, combine, opening night, etc.