then it has to do with how you're synching messages. go into an account, click on settings and the labels. number of days to sync can be any number, but inbox and sent or whatever else needs to be more than 4 days. i have mine set to sync all and i have every message ever, from my gmail account.
My settings are:
Duration-
Number of days to sync: 5 days
Labels-
Inbox: sync all
Sent: sync all
work email (non gmail): sync all
I've had those settings since I got the phone and the gmail account currently shows 41 emals in Inbox, but none are showing the the gmail app. When I check gmail on my Mac, I can see all 40 emails. I hit refresh a few times on the phone's gmail app and they still are not showing up.