These are starting to pop up at Costco's all over; my local one just got a giant pallet of them in.
They appear to be HD20's but there are some subtle differences: For example the published specs on the HD20 give a 4000:1 contrast ratio, for the HD180, 3500:0. I know what manufacturers report and what reality gives often differ however this seems to suggest either the contrast is slightly lower on the HD180, which would mean they are using a different TI chip, or perhaps Optoma just decided to publish specs that better reflect real-world performance, I don't know.
Also published noise levels for the HD20 are 32/34db in regular/bright mode - it's known to be a noisy projector. For the HD180 they claim 29/31, which probably means they are just using a different fan. Still fairly loud.
Other than that most other specs, including dimensions, weight, throw, lumens, etc, look the same. So call it a "HD20 lite" if you like
The thing is, the Costco price I see it for is actually a little more than what you can get the HD20 for online, so unless a couple DB (claimed) noise reduction means that much to you this really isn't that great a deal. Now, if they put these out there for like $799 or something this will be the steal of the year but that isn't looking likely.