General app question

sorry if this seems like a stupid question, but I know nothing abuot Macs.

Am loking to pick up one of the new MBAs, but may also replace my current desktop later this year or so and love the look of the iMacs. Are the Mac apps like the apps for my iPads? I mean are they tied to my account and not the actual computer. Could I buy an app for the MBA and then later redownload it to the iMac or would I have to rebuy the app?

thanks for helping a newbie out.

 

thanks thats what I was hoping for.