AH come on - the amount of space it takes up is near zero.
And besides - regadless of it taking up space, some people simply will not buy a device if it does not also include a radio (Me for one !)
If it had a radio they could sell a lot more units - and as a result sell more itunes given teh extra number of umits in circulation - albeit with teh average number of itunes being downloaded per person decreasing (which i strongly suspect wouldn't be the case anyway - at best a minimal difference).
And aside from teh ipod - how come they don't include it on their iphone?
Obviously it seems to be some applie policy generally accross their products.