I suspect it has a lot to do with 1.x was intended as a near "proof of concept" for lack of a more accurate way to describe the developers intentions.
A developers word to his users, in my opinion is more important than the software itself. Second is support. Third is the software.
I use some less than ideal software because support and honesty are top notch. I am about to abandon some excellent software because support is poor.
The second a developer does not keep their word, they become unapproachable. They become no different than Apple, Adobe, and the rest of the big guns who we must resort to mass group petitions to get a PR based appology.
By Allan keeping his word, he maintains something few ever pull off, which is being with us, not against us.
As I have mentioned, there will be nothing preventing any if us from ignoring the free upgrade option and just buying version 2 outright. No donation button needed.
If you really want to make it known to Allan you have chosen this method, we should simply come up with a plan to enter in "donation" as our middle name when ordering, or maybe as a comment if there is such a field.
I personally don't care to make it know. Allan will know when he checks his bank account :)