Having gently caressed its crystal balls, research firm iSuppli has released a forecast of Wii, Xbox 360 and PS3 "installed base" over the coming years. As is an analyst's wont, it's the typical platform war fodder that sees PS3 dragging its heels behind both rivals until mastering the 360 in 2010 and the Wii a year later. However, tucked away a the end is something a little odd - the report predicts that come 2011, the Wii and Xbox 360's installed base will mysteriously diminish.

The graph, pictured, shows the Wii a hair's breadth from the 40 million figure for its installed base in 2010, but experience a puzzling drop to around 37.5 million in 2011. Similarly, the 360 hits 33 million in 2010, before shedding around half a million users in 2011. The PS3, meanwhile, just keeps on climbing, amassing an installed base of 38 million - the largest of the three - by 2011.

There are a couple possibilities that spring to mind. One is that the apparently endemic Red Ring of Death takes its ultimate toll while Wii owners' interest in sport and fitness games runs out of steam.

The other, most logical explanation is that 'Installed Base' actually means 'Installed Active User Base', with iSuppli furiously polishing that crystal to predict the rate at which the installed base atrophies as users put the old dog in "storage" and move on to the inevitable next generation. This looks entirely credible given Microsoft and Nintendo's treatment of it's last-gen offerings, with Xbox, Gamecube and N64 effectively forgotten by their makers once next-gen fever took hold or the inevitable was resigned to.

Even giving the analyst the benefit of the doubt, however, there is another glaring problem with iSuppli's figures.

The graph shows Wii sales at 18 million for 2007, which doesn't match the actual figure published for end of 2007. As of December 31st last year, publicly available information showed that the Wii's installed base was in excess of 20 million. SPOnG has contacted iSuppli for clarification on why its figures do not reflect this information.

If you want to read iSupply's predictions for the future, you can find them here.

If you can explain why a market researcher isn't using publicly available information, by all means let us know in the forum.