Unlikely...at least 15 more million sellers are coming.
Remember: PS2 had a price drop by this point (May 2002, in its 20th month) and Wii monthly sales are still topping PS2 (which was cheaper than Wii after the price cut) in month 21.
Wii is going to do something like 9.5m to 13.5m in the Americas this year. Next year should be similar once the motion plus makes the Star Wars/boxing/swordfighting games accessible to everybody.
Wii shipments are outpacing DS and PS2 lifetime shipment totals by millions. PS2 is at 132m shipped, and DS is going to ship 100m+ in under 5 years. PS2 shipped 100m in 5 years 9 months. Wii is showing no signs of slowing down. For all the talk of Nintendo not releasing much in 2008...the year is going to end up with Smash, Wii Fit, Mario Kart, Rockband, Guitar Hero Aerosmith, Warioland, Tales, Mario Superstar Sluggers, Madden Wii-ized, NCAA Wii-ized, Boom Blox, De Blob, Shaun White, Guitar Hero World Tour, Call of Duty 5, Rayman 3, Starwars Clone Wars, Skate It, Need for Speed, the Castlevania fighter, Rockband 2, Little King Story, Sonic Unleashed, Face Breaker KO Party.
Every one of those games should sell 300k+, 90% over 500k+ and probably 60% of them will top 1m.