Yes, because when IE was the dominant browser that was totally the case.
Don't forget that on mobile platforms, not including Windows Phone, WebKit is already the standard engine. Safari, Android's stock browser and Chrome all use WebKit and developing for mobile is a ghetto, especially because each version has their own quirks and bugs (and there are dozens of Android stock browser variations in active use at any given time).
Yes, but just because there is one engine, doesn't mean there is one standard. Just like during IE's monopoly there were several versions of the browser to deal with (each with their own quirks), an engine monoculture (Webkit or otherwise) does not guarantee ease of development at all.
I agree that if there is to be a rendering engine monoculture, it might as well be open source, but that in itself guarantees nothing.
IE was dominant on one OS. It wasn't dominante on anything else than Windows world. Please, and that dominion lasted no more than 10 years. It ended with Android and iOS.
Windows was (and still is) the dominant desktop OS. Until recently, it was a very dominant dominance, with competitors usually making up less than 5% of the market share.
Even today, mobile users typically account for only about 10% to 15% of a site's traffic, for sites that don't directly target mobile users. Mobile just isn't as important or widespread as a lot of people think it is.
I don't know wich sites you are watching. All the sites I do control mobile is rocketing away from the desktop. Last year it duplicated. This year looks like it will be higher.
It gives a good sense of the current situation. Mobile browser usage is under 15%. It's nothing compared to the usage of desktop browsers. The growth from 2011 and 2012 isn't even that impressive, given the all of the hype and attention surrounding mobile.
Don't forget that on mobile platforms, not including Windows Phone, WebKit is already the standard engine. Safari, Android's stock browser and Chrome all use WebKit and developing for mobile is a ghetto, especially because each version has their own quirks and bugs (and there are dozens of Android stock browser variations in active use at any given time).