Apple’s decision to make Snow Leopard an affordable OS upgrade is paying dividends, with NPD reporting the new software has outsold sales of both Leopard and Tiger in just two weeks.

Price - $29 - is certainly part of this success, while the fact that a Leopard disc isn’t technically required to enable a Tiger user to upgrade all the way to Snow Leopard is bound to help, despite Apple saying this isn’t permitted.

As we reported last week, we’re certainly experiencing the same mass migration, with our current visitor stats showing over 62 per cent of 9to5Mac readers are already using Snow Leopard, while 29 percent are on Leopard, as indicated in the chart below. 

That 62% Snow Leopard users is up from 55% the week after release and 10% the day of release.  This is substantially faster adoption than we saw with Leopard.  Three months after Leopard was introduced, more than half of our readers were still using Tiger.

As reported by LoopInsight, Snow Leopard sales in the first two weeks have “far exceeded” those of the two previous OS’s. NPD believes Snow Leopard sales are over twice those of Leopard and four times higher than those achieved by Tiger.

Sales also remain steady, as second draft upgraders move to but the software following Apple’s recent release of a patch to address issues encountered by early adopters. Snow Leopard sales declined by 25 per cent, but fell 60 per cent for the previous two OS’s.

“Even though some considered Snow Leopard to be less feature-focused than the releases of Leopard or Tiger, the ease of upgrading to Snow Leopard and the affordable pricing made it a win-win for Apple computer owners — thus helping to push sales to record numbers” said Stephen Baker, vice president of industry analysis at NPD.