In my opinion it doesn't absorb as well, especially for people like me who have medium length hair as a lot of it just gets lost in the hair.
Liquid minoxidil with Retin gives me really good results, whereas Foam doesn't give me any at all.
Saying that I still use foam in the morning just in case, and because I think it actually helps my hair look a bit thicker once its dried, but as for actual regrowth from it... well none would be my verdict (and thats even on the bits where I have no hair).