These two projectors have much in common. Both use 3LCD technology - 3 separate LCD "chips" or panels (call them what you wish), one each for red, green and blue, and then are recombined using a dichroic prism. With the exception of Sony (which still produces some LCDs for their own use), Epson is pretty much the only supplier of this type of LCD technology. You'll find their panels inside all the 3LCD projectors except those from Sony. In fact both projectors are using the same LCD panels, and that has a lot to do with their relatively similar performance.
Both projector offer extensive placement flexibility, both are dramatically brighter in their brightest modes, compared to their "best" modes. Both offer one of the new "gimmicks" - creative frame interpolation, now found on only a very few projectors.
Getting the idea? These are two very direct competitors, and both have to be counted in the top three of 1080p projectors in terms of sales.
Significant differences include overall brightness, black level performance, and warranty, and of course there are a host of minor differences. Let's break them down by category.