I suppose it can happen, it's not impossible.
2006: 1.2 million
2007: 7.6 million
2008: 9.6 million
2009: 12.7 million
2010: 15 million
2011: 17 million
2012: 15 million
2013: 12 million
2014: 10 million
2015: 8 million
2016: 5 million
Total: 113 million, seems somewhat reasonable, we'll likely see the PS3 at $199 or less in 2011. Along with big exclusives and constant updates, new features, and peripherals it should keep selling at a good constant pace.
As for the Wii, the only reason it'd stop selling at 103 million, is either a new console (HD) in order to try to steal some 3rd party devs from X360 and PS3. Or it'll actually slow down and sell worst and worst from now on, by the looks of it the Wii may have already peaked.