>As a contrived example I'd probably be perfectly happy if I could only browse, read, and maybe vote on HN if the mobile experience of reading was significantly improved. I never want to write a comment from my phone, I hate typing on it. Not a great example since a textarea isn't complex and it's easy to add to a mobile layout, I just want to get across the point that not all interaction is appropriate or important on every platform.

But you didn't get across the point, because your example isn't true. I want to post on HN from my phone; heck, I've posted on HN from my kindle before. I wouldn't give that up for all the optimized mobile design in the world.

Grandparent is right, an absolute is appropriate here. Provide all the functionality of your desktop site, or I won't use your mobile site.