I put this in the Crackberry thread about BBM on WP, but I'll repost it here.
Last month, the place where I work was deciding on what IM app to use since it was easier than emailing and our IT guys aren't really fond of excessive emailing (they're kind of anal about it actually). We were going through the options at a meeting where all of us attended and someone in our group suggested BBM (side note: I've seen at least 5 Windows Phones in the wild, yet this guy was the only person I know who has a BB10 device. I'm sorry if that doesn't line up with what you see, but I have seen 1 total), which is when everyone was like "oh, yeah, that's on all of the phones now" and everyone was feeling a little nostalgic until I pointed out that myself and one of the managers had Windows Phones (I have a 1520 and he has a 920) and that BB doesn't have an app for WP. Do you know what happened? Did they tell us to get new phones? did they offer to buy us cheap androids? nope. What happened was that we canned the idea of using BBM. One girl even made the exact quote: "dumb Blackberry, I thought they were suppose to be a billion dollar company, I didn't realize they're that poor". In the end we decided to use WhatsApp and BBM lost about 20 potential new active members.
See, here's the gist... Yes, Windows Phone only has an 8% market share worldwide, but do you know what that means? That means that unless someone has very few friends, that they all know at least one person who has a Windows Phone. Now I know that a lot of people here claim that they've never seen a Windows Phone ever, but they usually then go on to say that WP is DOA and they know at least 20 friends with BB10 devices, so those comments can be thrown right out.** I'm trailing off again, but this basically means that if people want to use a cross-platform messaging app, that they can't use BBM because one or two of their friends don't have it.
Now it's simple to say "oh, well, then they'll leave WP, because it $ucks M$ herp derp"** but come one now.... People will change IM services before they change OSes, because guess what? Most people don't care what they use, as long as it works. Is BBM great? yes, but is it so great that it's worth learning a whole new OS (even if it takes minimal time) and repurchasing apps? no. It's the same thing as my company. Most people didn't care to use WhatsApp and since then I've never heard a single complaint. They even WANTED to use BBM, but since it wasn't cross-platform, they couldn't (and they even got mad at BB for it, so double-lose there). I completely understand the reasoning behind it, but they need to get BBM to WP pronto, even if it's only half-baked in features.
** yes, they were actually writing stuff like that