Perpetual Upgraders - Why do you upgrade so much?

Aside from the fact that many (most) of us on this forum are tech geeks, many of us upgrade devices quite a bit. My upgrade path, starting in June, 2010, is as follows:

June, 2010: Original Evo 4G on Sprint. I made the move after being on AT&T with a Nexus One for a few months, mostly because AT&T 3G was suffering quite a bit at that time.

September, 2011: Samsung Galaxy S II Sprint Epic 4G Touch - phew. Anyways, the Evo was getting a bit...old. Got tired of having to load up ROMs for the device to be fast.

Late Fall, 2011: Samsung Nexus S 4G - I was able to get a basically new Nexus S 4G for around $200 (no contract, through Craigslist), so I jumped on it. I ended up selling it a few months later for the amount I got it for.

February, 2012: GSM Galaxy Nexus - Sprint 3G and WiMax by this point was terrible. So I decided to try T-Mobile's $30 prepaid plan w/5GB of data and I wanted to get back on with a Nexus.

December, 2012: Nexus 4 - because it's the newest Nexus!

June, 2013: HTC One - I wanted a new device, I wanted T-Mobile LTE, and battery life wasn't great on my Nexus 4. I found out about the $100 tradeup offer, so I decided to try out the One. After a week or so, I ended up really liking the device and use it now.

So in 3 years, I've gone through 6 devices - average upgrade cycle of 6 months. I upgraded a few times out of necessity or because of a good deal, but usually because I just wanted something new to play with. How about the rest of you? How often do you upgrade, and why?