They are not the unstoppable force that they were before but I think that calling them irrelevant is a bit too much.
Or look at it this way: It's not about selling a phone OS. It's about the ecosystem behind the devices.
If you don't think Microsoft's ecosystem is competitive, it tells me you haven't tried it.
You probably will never come across them, but one of my cousins got a Lumia, and made the mistake of not lying when registering the phone.
She ran afoul of two things:
1) Marketplace simply does not work if you're a minor
2) Almost nothing works if you set your place of residence to Uruguay.
So I had to create a false account for her, and reset her phone twice, before she had a passable user experience.
It might "work" if you live in the U.S., but I absolutely do not recommend it for small third world countries, and will only recommend Android here.
Btw, I'd add a third caveat:
3) Most software doesn't have "free" alternatives like on Android (absolutely deal-breaking if you don't have access to a credit card, which most Uruguayans don't)
It's sad, because the hardware beats the crap out of Samsung phones, the UX is better, and I love the Camera button. Too bad Nokia chose Windows, I loved my Nokia phones (still use one, an N86).