Then again, it's not like you can store 0.1.3 as a float.

On the other hand, some version numbers can be stored as floats (kind-of, to a point): Knuth's software is versioned using approximations of irrational numbers, the more digits the later the version. TeX's current version is 3.1415926 and METAFONT's is 2.718281. Both can be stored as floats, although the respective and eventual π and e can't be.

I think you're thinking about decimal expansions, not IEEE 754 floats. Most (almost all) prospective TeX version numbers cannot be stored accurately as floats, but they can as decimal expansions.