I disagree. It doesn't make sense that rounded-end tenons would loose
rigidity more so than squared tenons, when, at some point in the very
distant future, the glue finally fails.
I have no experience with other rounded tennon/mortise systems and
cannot comment on them, but the multi-router (as was mentioned here)
works within incredibly tight tolerances. The resulting joints are
sized within a few thousands of an optimal fit - and consistently so!
A proper fit, is in my opinion more critical to the longevity of the
(mortise/tennon) joint than is its shape.

Darrel - The Greene and Greene rocker is looking very nice!