The Huffington Post article (huffingtonpost.com) about iOS apps that upload contacts in the clear & store them on their servers is pretty concerning. Where I grew up, this would have been considered totally inappropriate & scandalous. I'd be outraged if I'd had this done to me. As it is, I'm glad that most of the people I help with their stuff aren't big into the social networking stuff, so should be OK.
Not OK, & never would have dreamed that anybody else would have thought it would be!
Do we know why the reference article (& its embedded references) cite iOS, & all call out iPhone specifically, but don't mention iPad? That certainly has a whole set of contacts information.
Interpretation of the file extension is on the client side and should generally be case insensitive. Bear in mind that file extensions go all the way back to the DOS days and that DOS was an entirely case-insensitive operating system.