Strongly agree. It seems odd that desktop UI designers haven't taken that route (although if you look at the default MS Office icon suite, there's a clear intent to consistently visually separate data and executable files.) Ultimately, the user doesn't want to decode a three-letter extension, so why are we even considering forcing them to? The actual problem is simple and only needs to deliver a simple binary distinction between two specific classes of file.
The days of computers being 'for' techies are long, long gone. I strongly suspect that the
Remember the way old iOS icons used to use a very distinctive button shape and highlight across all iOs apps? That kind of approach would work well to make applications stand out, and then do something similar, but distinctively different for all data formats. Apple have had no problem with setting strong UI guidelines in the past. I'm not advocating the specific glossy-button - just a consistent aesthetic approach.