The 500 lumen projectors being released by Optoma, Acer and Viewsonic are not identical. Although the projectors seem to share a 'base', they do have distinctive differences. As anyone else in marketing would know, it is not a good idea to push out a product with the same specification as your competitors, to be released at the same time, at the same price. The only differentiating marketing tool would be your company name. It would not make for a smart business decision.
There are differences in connections, 3d functionality, and contrast ratio to name the few that we are aware of so far. I highly doubt the differences will end there!