I have heard Peter Greenberg say that particularly in High-rise hotels, there are "pumping stations" every 5-10 floors to push the water up to the top. The closer you are to that, the better the pressure. I have also heard that you can ask where these pumping floors are at check in and ask to be roomed somewhere close.
I've never had this problem before at hotels. The best shower I ever had was at a hotel, the Westin in Sydney Aus. The hotel is in what used to be the old post office. The ceiling was about 10-12 ft. and the shower head couldn't be reached. It had a "watering can" head that was about 1 foot across, and was like standing under a gentle waterfall... it was truely wonderful... thanks for reminding me... :-)
BB