Apps show in Market on PC, but some not showing Market on tablet

[Murf]

I can search on Market on my PC and find an app. Then when I go to my tablet Market and do same search, some of the apps do not show. If it just so happens I find them in "related apps" section of another app and get to them, then there is no "download" button to get to them. (A direct search with exact name of app will not even find them.) What's up with that?