I hope the link works properly this time:
It should say:
The built in Round Corner effect in Illustrator will preserve the shapes if you add anchor points near the corners of the rounded curves - basically limiting the radius manually. Another thumbs down for the built in capabilities.
Yes, sign industry apps like FlexiSign have had the capability for many years; even long dead apps like CASmate did it. Even CorelDRAW has a filter for doing corner fillets, scallops and chamfers. You could apply the effect to specific corners in addition to altering all the corners on an object.
I think the corner fillet/chamfer/scallop function is a basic enough feature to warrant inclusion in the stock Illustrator tool set.
Considering Illustrator CS6 is going 64-bit, I'm leery of paying money for any existing Illustrator plug-ins right now. A lot of plug-ins will probably have to be recompiled for 64-bit operation in order to work. Existing plug-ins might survive if CS6 includes both 32-bit and 64-bit variants of Illustrator.