Google.com has quietly improved its filetype: searches. Previously, it was looking (simply) for the part of a page URL that ends in the filetype: argument, and it can still do so:
filetype:tonini (finds Facebook profiles in particular).
However, for standard, common file types, Google now also searches for all files of a given kind (such as MS Excel), with a variety of extensions. I.e. Google now searches according to the “true” file format (vs. just the string in a URL after the last period). For example, consider this search:
You will be finding MS Excel files