Looking at the DateTimeFormatInfo documentation, it appears that all the standard formats have colons in them, which makes passing them on a url unpleasant/impossible.
For what it's worth, ASP.NET MVC won't automatically convert ticks to a datetime either, which surprised me.
There's a constructor for DateTime that takes the number of ticks:
DateTime d = new DateTime(634028202671420663);
There's also an override that lets you map that to either local or UTC time. It's all in the docs: http://msdn.microsoft.com/en-us/library/system.datetime.datetime.aspx
Edit: realised from the wording of the post that perhaps you're talking about ASP converting the ticks automatically to a DateTime, rather than having to read the numeric parameter. Perhaps! :-)