The hash rate shown on the account page has been consistently 20-25% below what my miner tells me it is, I never really gave it much thought. One or the other, or both, are wrong.
Well, that hashrate on the profile page is just an estimation; hashrate given by your miner will be much more exact. Actually as far as you don't see any connection issues in the miner, don't worry. Pool indicates accepted or rejected shares directly in getwork response, so all possible issues should be catched by your miner.