Okay, even if it was free, there's no reason to think people would be tripping over themselves to download the new album. Neil Young gave away all of Living With War. What percentage of people who consider themselves to be Neil Young fans downloaded those songs? (And Living With War turned out to be a pretty good album.) Memory Almost Full is available from eMusic for $3.50-$4.30, depending on your subscription level. That's less than $1 in 1973 dollars -- to use a frame of reference that most McCartney fans can identify with. You could buy the album for about what it cost to buy "My Love" as a single. Whatever McCartney's challenges are in selling his album, cost seems to be a minuscule factor.
And McCartney was perfectly capable of phoning it in even back in the days when "everybody" was listening. Remember Red Rose Speedway? Wild Life? Memory Almost Full was stronger than many of McCartney's albums from his commercial peak (post-Beatles), so -- for once -- we can't accuse him of being unmotivated.
And 550,000 units in the U.S. alone sounds pretty good for a 65-year-old pop musician. That probably translates to over a million albums sold, worldwide. The last.fm numbers for "Dance Tonight" -- the lead track on the album -- are very impressive, leading all other McCartney or Wings songs in number of listeners over the last six months.