In business theory, there is the concept of the product life-cycle which has a massive bearing on long-term viability:
This is a very over-simplified version (there are many variations on this model), but nicely details what each phase of the product lifecycle entails.
So Windows Phone is now entering the "Growth" stage, which basically secures its long-term viability.
Essentially if a product makes it out of the "Introduction" phase to enter a period of fast growth, then the company will ramp up investment. This is why you are seeing Nokia and MS pour millions of pounds into advertisements and product placements. Its seems counter-intuitive (surely a company would spend this money in the "Introduction" phase??) but the reason behind this is that early-adopters (i.e. mobile tecchies in WP's case) are introduced to the product first. If they had disapproved, MS/Nokia would not look to invest heavily in the product - but given their approval, its believed the product will make money, so investment increases to reach the mass market and its long-term future is secured.
If you think of WP7 and the initial introduction of WP8 as being in the "Introduction" phases (informing and educating the market on this productline), you can see how they now fit into the "Growth" phase. Nokia is targeting developing markets in a bid to rapidly incrase market share; the advertising campaigns are focused on differentiating the product from Apple/Android (WP is "built around you", all the memes about cameraphones etc), there is significant investment in promotions (Man of Steel sponsorship, celebrity endorsements), and of course widespread availability of the devices now.
In contrast to Apple, who endeavoured to sponge the "Growth" phase for as long as possible (they are now entering the tailend of the maturity phase), it seems the aim for WP8 is to grow the product as quickly as possible to get straight to the maturity phase. According to the model,WP should have entered their growth phase when the iPhone 3G or iPad was released, which is when industry competition is at its peak. It therefore makes sense they are rapidly pushing the product to the Maturity phase now, as where the product becomes a cash-cow and is seen as a genuine competitor to Android/apple.
Its like being back at University...!