There needs to be a Keynote Player (Windows and Mac) and I am sure Apple is working on it (or I would like to think so). Without the player Keynote's usefullness is more limited and it may not achive the desired penetration either.
IMHO, it would be a mistake to handicap Keynote player for Windows ... since that would just create a bad image for the creator application for those people that never used it.
We sould not underestimate the need of a Mac Keynote player as well, which is much needed for the following reasons:
1. No need to fire up Keynote, just to play your presentation. (Like opening Acrobat Reader, rather then Acrobat itself).
2. To be able to watch presentations, even if you don't have Keynote app.