I follow what I need and my budget - almost always buying phones outright, up front and then using whichever carrier suits my needs for service: sometimes networks get poorer coverage or capacity, so I like to move on, without penalty.
As we've seen, buying a phone upon launch means that you pay considerably more than after a delay, as the price drops. There will be new phones coming, some of them better than what's out there - but I think it's best to invest wisely which, for me, means that I get great use from each handset, including using them sometimes until they're almost dead. I may miss out on some new releases in this time-frame but, when I do upgrade, there's usually a fantastic lift in specs and performance. Stick to networks' contractual timeframes for upgrades, or make your own, based on your budget and expectations? 2 years is a reasonable timeframe but maybe it doesn't suit you. In the UK you can get 1 month, 12 month and other periods of network use only contracts - this varies depending on your country and I'm guessing that you're in the US.
What we have learned is that MS is interested in targeting the business market with their windows phones, coupled with 3rd party manufacturers, such as HP, who'll probably do much of the same in the near future. This is likely to keep equipment prices up, so I think it's greater motivation to ensure that the investment is efficiently utilised.