Tom's right, you should be comparing to the indie license. Also, Game Maker is a scripting based tool, so you need to learn a programming language to use it. Construct is an event based tool that does not require you to learn to program to use it, so the barrier to entry is lower. People who already know how to program are probably happy to stick to programming - we're aiming Construct at people who don't know how to program, which is why events are useful. However, it's much faster than programming, so some programmers might like it anyway (which is true of our experience from 0.x).
So why worry about Game Maker? If you want to program, there are tonnes of alternatives out there, and you can even program a HTML5 game for free in notepad providing you know javascript, the correct APIs and so on - but it will take a lot longer and require a lot more expertise! We're not expecting hordes of Game Makers to jump ship either, because most of them are very familiar with the GML scripting system which is how they make their games, and there's no equivalent in Construct 2.
This is probably also a large factor for new customers. Are you really going to choose Game Maker over Construct 2 solely because of the price, and ignore the fact you have to get in to programming to do anything useful with it? They're actually completely different products with totally different features and methods of working. You should bear this in mind when making comparisons.