Odd - I batch erase emails all the time on my iPad (and my iPhone). Quite simple to do, if one wants to.
With 5000+ emails stored from over several years I have not found an easy way of deleting all emails over 6 months old as an example.
I use the iPad mainly for an aviation application and for email on a trip. When it's switched on after a period of no use I have to wait while it catches up on the missing month or so of email, with no good junk mail filter like my PC at home.