As an amateur pilot, it sounds like this was an unfortunate course of events, but was handled properly. For example, when the altimeter stopped working, it was the right decision to turn back to Heathrow. When the second plane was deemed not airworthy, it was the right decision to not fly it. There are many reasons why an airplane can be unsafe to fly, and it's not always possible to prevent these incidents from happening, even with good maintenance. The best that can be done is thorough preflight checks while on the ground, and an emergency landing if issues crop up while airborne, however slight.<p>I'll concede that American Airlines could have treated its customers with more courtesy, offering them food and drink. It's certainly possible that American could have performed better maintenance on their planes. But it's good to know that their pilots are safe, and won't risk flying over the ocean if they have a slight (realistically irrelevant, given GPS) instrument issue.
Heathrow has always been terrible for me - except once, when I entered the UK from New Zealand without showing anyone my passport. I didn't even get it out my bag. This was pre 9/11 but it weirded me out so much that I nearly walked back to check with someone that all was ok.
I will go to just about any length to avoid LHR. The only exception being when I am actually terminating in London and not transiting. It is really the most intentionally wretched airport I have ever visited, although they're all miserable in their own special ways.