Software provides you with a *service*, and there is nothing unusual about subscribing to a service. Many of us pay Apple annually for .Mac, providing us services -- synchronisation, calendars, remote backup. We subscribe to websites, such VersionTracker. We also see products like Quicken begin to embed value-added, subscription-based services.

The way I see it, this product adds a bit of value (compared to the free alternatives) via the archive function, and seems quite reasonably priced as an annual service fee for maintaining an archiving, bootable mirror.