[TillE]

Yeah, assuming your software is reasonably modular and you haven't completely rewritten everything from scratch in the new version, retaining support for old file formats shouldn't be a very big deal.

At worst (like in the case of iWork 13 which probably is completely new code), you get one programmer to spend a few days writing a converter which reuses most of the old code.

[XorNot]

More importantly, provided you don't do it too often, users will tolerate some loss of formarting fidelity from version to version.