Except the argument was that the general public aren't fans of Windows phones, to which 20% market share of a few regions was used as a counter argument.
I would tend to think that market share is one indicator of a phone platform's popularity, and while 20% is not bad, it's not an amazing figure either.
I looked around for a chart of the iPhone's market share by year, but couldn't find one. I remember the iPhone having trouble in its first year or two, and most of WP8's credibility comes from the ~2 year old Lumia line.
True. In 2010 the iPhone only had about 4% market share. My only point is that I'm talking about popularity of existing devices. It may well be that Microsoft will turn it around!
The other way to look at it is that iPhone had ~100% share of the "modern smartphone" market (choose your own name for it, but Blackberries and Symbian don't count).
I would tend to think that market share is one indicator of a phone platform's popularity, and while 20% is not bad, it's not an amazing figure either.