I'd believe it. Mainly because MS is going to (heck, already is) marketing the heck out of their tablets. So they will pick up some market share. Maybe not as much as they'd like though. A few of my tech-savvy friends ah "in the younger generation" shall we say see the MS offerings as overpriced.
But marketing $ typically work, at least a little so I expect them to increase. On the other side of the coin though, Apple people tend to be very loyal to their brand. I wouldn't expect too many to jump ship. The small amount that does will probably be made up for by new converts. So I would see Apple holding steady.
The new consumer base for the developer just grew by well over 100,000,000! App shortages will disappear rapidly.