4.1 has also a acquired a less-than-fetching, default hair-do and a fuzzy bikini, which appears to be based on the one Raquel Welch wore, 1,002,007-and-a-bit years ago.

A lot of vendors do specify 4.1 as the requirement.   I don't know how crucial that is.   If you have 4.0 already (and not 4.1), you should ask DAZ to re-set your download.   There is no cost to downloading 4.1.  

The 4.1 base geometries need to be in the main Poser runtime, as opposed to a V4-specific, external run-time.   I think that everything else can continue to be directed to an external runtime, if you are using one.