For me, the significance of this is that the US Govt have jumped on board. It says that they want a piece too.
If people have read around on this subject they'll know that it's not an easy case to prove. It'll need to be shown that the USPS were actually damaged by Armstrong et al's fraud. It seems Armstrong et al could own up to fraud yet get judgement in their favour because nobody actually suffered any financial harm. I find that weird but whatever.
A lot of these whistleblower cases are apparently settled out of court but, as the 2 parties have already been in discussion for some weeks, maybe that won't happen.
I'm wondering (and this really is just me 'what if' thinking) if one of the purposes of this case is to get Armstrong in the witness box under oath. The whistleblower case might go in his favour but who knows what his testimony might open up.
One thing does seem clearer to me, the US Govt would not have taken this action without confidence. They've not got the best of track records when prosecuting athletes so I feel they'll be pretty certain of themselves here - whatever their objectives.