I'm a bit confused as to why you have to ask - look in any of the 2.1 threads and it becomes pretty apparent and these arguments have been well rehearsed (on both sides) over 100 of posts in this very forum. It wasn't supposed to be trolling ("i'll bite"?) just a fairly common point of view amongst (ex in my case) Hero owners.
But just in case... by horrific communications. They skipped the 1.6 update to wait until 2.x, but then, after confirming the 2.1 release they spent a few months until they confirmed when it was to be released. Rumour after rumour hit the internet, some apparently from HTC's own customer service. HTC could have done what any normal company usually does and say "you will have 2.1 by x".
They did eventually, but way too late to make it look as though they had the faintest idea what they were doing. Some say that HTC are under no compulsion to release 2.1 for the Hero, and arguably they have a point (although if they don't that makes HTC Android phones not very attractive - back to the thread), however they did say it would be coming, they didn't say when until too late.
A really basic error from HTC and one that has a whole load of people (whether you like it or not) thinking carefully about their next HTC phone rather than it being an automatic decision. I eventually decided to give them one more chance and got a Desire - but if we see the same mess again then that's me done. I'm not unusual in this view.