I also suspect that the very poor standard of VFR FPL's in the UK (not of course by you dear reader) might have had a bearing. Because VFR plans were simply faxed to the destination and did not enter the AFTN the non-conformities to ICAO standards did not cause a problem. Those who have been filing IFR through CFMU will be well aware of the need for higher standards of production.
Worth mentioning that the inability to use 4 letter a/d designators in a route (much derided by the proponents of Olivia) is an absolute requirement for any system for submitting FPL as 4 letter designators are not valid in an ICAO FPL route.
I don't see how AFPEx (or any other electronic service) changes the ability to insert any old crap in a VFR flight plan.
The FP is just an AFTN message and nobody cares what it contains. You could file a VFR FP with waypoint called "Samantha Fox" and the system would transmit it to the specified addresses, just fine
IFR flight plans are validated by Eurocontrol, which is nothing to do with the issue here. Eurocontrol do this because IFR FPs are addressed to them and to nobody else, and they re-distribute them to the units along the filed route.
It is rather academic now but I cannot help wondering why electronic FP filing has taken so long.
Regarding AFPEx, I think people should disregard the negative press which is all over the forums, from a small number of individuals who for the most part, as far as I can see, have difficulty with the internet and "IT" generally. The system has its faults (like the big Java download, and no feedback on IFR slots, and the Java app does not run on some/most non-windoze computers) but it works really well otherwise. I really like the way the message is sent instantly and, on IFR FPs, the feedback is similarly instant.
It is unfortunate that the PPL training process does not prepare people for the fact that practically everything connected with flying has gone to the internet and that their lives will be a lot easier if they get up the learning curve.