They are exactly the same and both come directly from Ambient. I think people are just accustomed to shopping directly on Amazon and Ambient is taking advantage of this and therefore the price is greater there. Ambient also has some costs associated in selling through Amazon. If you go direct to Ambient you are rewarded with a better price but shipping time will be a bit longer possibly.
For anyone considering the WS-2902A, I would urge you to consider the WS-2000 instead. Much easier to set up and many more features:
http://www.wxforum.net/index.php?topic=36379.0Realize that any current Ambient station is not compatible with your Cumulus 1 software. In fact you don't even need to keep a computer running depending on what you are doing with your data. Since you seem to be running your own website with Meteotemplate you are going to need some form of software. Since Cumulus 1 wont work you'll need to consider other software. I highly recommend paring a WS-2000 (or WS-2902A) with an Ecowitt GW1000 and then you can run Weather-Display or a Meteobridge device or WeeWx software to keep your website up. The GW1000 isn't absolutely necessary but it is a way better way to go that to intercept data from the WS-2000 (or WS-2902A) or than to rely on Ambientweather.net API.
