Key lengths for algorithms for variable-length keys

[Ben Harris <bjh21%bjh21.me.uk@localhost>]

transport-23, in section 7.2, says:

   128 bits (16 bytes) MUST be used for algorithms with variable-length
   keys.  The only variable key length algorithm defined in this
   document is arcfour).

Apart from the mismatched parenthesis, this seems like a strange 
pair of sentences.  The "arcfour" algorithm as specified in section 6.3 is 
defined to have a 128-bit key anyway.  RC4 does generally support variable 
key lengths, but so do Blowfish and CAST-128, so why aren't they 
mentioned?

If this stipulation is meant to apply to all future algorithms, it seems 
like a particularly bad idea.  Is it intended to prevent me defining 
"arcfour-256%bjh21.me.uk@localhost" to be RC4 with a 256-bit key, for instance?  If 
not, what does it do?

--
Ben Harris