They're both pop bands in my opinion, a form of group which seems to have almost died out in the advent of vocal groups and "trendy" guitar bands. Fleetwood Mac's great current album was simply a Lindsey Buckingham (guitarist in the band for nearly 30 years) solo album which never happened because Fleetwood was the drummer chosen by Buckingham. A bit like if Neil wanted Paul to be his drummer on his next solo album, not such a strange idea as they have both enjoyed working with each other before. What happens then, you bring in Nick Seymour who is obviously a good bass player and you've already got Crowded House back together even without the keyboardist and even without thinking about it. The only problems I see for this is attitudes, egos and perhaps geography.
It may be a marketing ploy by Buckingham, because his solo album would not have sold as much, but who cares as long as the end result is great! and it is 30 years on after he joined the band he's still making sweet music with them if not better! This rubbishes the theory that a band should exist for 10 years maximum (which I've heard said by Neil himself!)