Well, it wasn't suddenly, actually, only a few months after we released the first version, we released v1.1 which started the ball rolling on optional features and priority support. This latest v1.2 release just added two more pay-only features. Furthermore,
right next to where it says "Free", we put a link to the Licensing FAQ, who'se first question & answer is the following, and I believe this message was the original up-front message since day one:
Q. Will this product always remain free? Will I ever be forced to pay for an upgrade?
A. At some point in the future, for new users, the product may someday no longer be licensed for free. However, if you register before that happens, it will always remain free for you. By registering now, we will treat you as if you
purchased a paid license for the product. You will receive a registered license key which will continue to work in new versions, so you can benefit from bug fixes and even some of the many new features we're working on.
This isn't hidden away somewhere, it has always been up front (I just checked archive.org to be sure), and for half the product's life (the past 4 months) we have also put, right up front, this message and similar ones, to promote the advanced updates:
"Professional-level support and advanced updates available with Vanguard subscription"
And, as far as saying that "it is not cheap at all compared to competitors", currently, it is. The competing WPF offering's "product + 1 year subscription" is in fact close to double the $500 price of Xceed DataGrid for WPF's product + 1 year subscription.