This is curious...
I'm thinking this is Harlequin the bookstore reacting to their reduced ebook market share rather than Harlequin the publisher giving in to PiracyParanoia™.
I suspect they are only dropping ADE on their site and doing it as a cost-saving move:
the backend server and authentication costs for the webstore have a fixed component, in addition to the per-book costs. With the majority of ebook readers committed to one walled garden or another, the business isn't exactly friendly to independent ebookstores anymore.
This is worth watching because it reflects on the debate as to whether publishers should or even *can* start/increase direct-to-consumer ebook sales. Harlequin has been doing it for ages so if ADE support is becoming onerous to the store it would discourage other publishers, especially if they're wedded to DRM, unlike BAEN and other direct-sales publishers.
Alternately, it might be that HC is using Harlequin to experiment with Applocked ebook distribution to test consumer acceptance. Less likely since Applocked ebooks haven't been successful in times past. You'd think they would have noticed.
Worth keeping an eye out to see what comes next.