Yes, it is annoying but may or may not be an issue for end users. Tcl and Tk are themselves OpenSource and GPL compatible but their license is less stringent than GPL, which allows ActiveState to close up their version (which AFAIK only adds the convenience of a binary install). If you are bothered by it, compile from sources. This is what Simon Urbanek does for the CRAN Mac binaries.
Regarding legal issues, I believe this only bites if you both compile R against ActiveTcl _and_ try to redistribute the binary.
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Office: A 4.23
Email: [hidden email] Priv: [hidden email]