Sins and Demigod also had Collector's Editions. However, if you pre-ordered the digital-only version (which can't be collector's since there is no box), there was no way to upgrade to the CE box.
However, it has been stated somewhere that "someday there may be an upgrade button" that would allow people to upgrade to the retail (and thus collector's) box.
For the record, Stardock only sells the un-collector's edition box at retail outlets, and I guess when the collector's edition have out of stock. If you order the box directly from Stardock, and they have any copies of the collector's edition left (i.e. are a pre-order or early purchase) then you will automatically get the collector's edition. (this is what Ron was saying)