That figure--10 million--seems awfully high for a consumer product that's charting unknown territory. The tablet (or iSlate or iPad, if you prefer) would target an untapped market, if rumors of the device's form and functionality are true. True, a few tablet-style browser/media players are either already on the market or are arriving shortly, but none has garnered anywhere near the attention of the Apple tablet.
I did some checking at Apple's site to see what sales figures were like for the iPhone in its first year. Here's the breakdown:
Q3 2007: 270,000 units
Q4 2007: 1,119,000
Q1 2008: 2,315,000