Your apps are associated with your Google account so once you purchase and as long as you keep the same account you will be able to install the app after switching roms or phones.
Apps such as Mybackup pro and Titanium will back up apps. Most folks use them to keep any data that may be in an app such as txt messages, notes, etc. I may be wrong but my sense is you receive updates to the Davis Drug app and do not update. If, however you make notes in the app then a backup app would restore the notes.
mwhartman, thanks, I loaded mybackup pro on my newly rooted droid running on simply stunning v4.6. I saved it as an apk+data and it said it successful. Is there any way i able to check to see whether or not it worked, without risking losing my app?
Open the app, tap view, tap data or app (depending on what you saved you may want to look at both), tap local or online (which one you used), tap the backup you made, tap the filed and it will display what was backed up.
If you backed up your iPod with the games saved already then it'll restart from where you left off. Although you could never really know with Apple stuff.