At retailers, there are no checks in place to prevent unauthorized users from buying the software. Microsoft effectively removed any system to enforce that by offering the software in major retail stores. In fact, CompUSA, Costco, Staples and other retailers prominently display the academic and nonacademic versions side by side, making it easy for nonstudents to pick up a copy. The stores don't necessarily check student IDs the way an educational dealer or college bookstore would.The price break on academic versions of Office XP isn't trivial, with some retailers selling academic versions for 25% of the cost of their non-academic counterparts once you factor in rebates.
I'm all for giving students a break on software so they don't have to spend months on a diet consisting solely of Ramen noodles, but opening up academic software prices for everyone doesn't sit right with me either.