As a Wordpress user I can understand the blanket call for Wordpress intergration however, the main message we learn from the team at Unbounce, is that landing pages are completely different from a website. Unbounce go to great depths on helping us learn when it comes to all aspect of pay per click marketing. Its obviously a great system as there are now many companies trying to copy it. None of which go to the depths that Unbounce do, they merely copy.
The support and personal level of service I have received from Unbounce over the last couple of years is something that I have never found anywhere else, so be careful what you wish for
Setting Unbounce up on a sub domain isnt too hard and if you need help they will talk you through it. SEO reasons really shouldnt be relevant with a landing pge either because pages for your PPC campaigns should be completely seperate.
My guess is that people would like to use Unbounces optimised templates for their traditional website, but this shouldnt be that hard to replicate these days with all the various themes and click and drag frameworks etc.
Not trying to have a fight, just stating lets remember what Unbounce is created for, optimised PPC landing pages. They are very clear that they are not trying to do several things averagely, but one thing brilliantly
p.s will be interesting to see what Wordpress intergrations you guys come up with