Everybody is entitled to their own opinion of course, but just looking at the fact shows this cannot be true. If both bands had "millions of fans worldwide who buy everything" (and let's tone that down to the major album releases on either vinyl or CD), their latest albums would have sold millions of copies. However, they didn't.
Even though the number of records sold figures that you can find online should be taken with a pinch of salt, PSB apparently sold 50 million albums worldwide and New Order just over 3 million albums in the UK and US (their biggest markets). Let's say a PSB fan who owns "everything" owns all 25 albums (studio, live, remixalbums etc) in multiple formats (all albums on CD, further listening, most on vinyl, let's say 50 albums in total, not even everything) then at most there could have been 1 million hardcore fans in total worldwide during their long careers (there were simply not more records sold). But of course the general public bought a lot of those records too, and I am guessing that would make the majority of their sales. And some of their albums sold only a few 1000 copies (Disco 3 less than 3000 for instance). For New Order that will be way less even and both bands do not have the majority of fans in the US. So hardcore (and still active!) fans of either band (with an overlap as well) will maybe fill one arena or less on a US tour. That is why they have to appeal to the average Joe and play the hits/best-known songs.
I would say for acts like this, there are worldwide a few thousand hardcore fans who buy "everything" (as in most releases).