PPC login puzzle

[Charles Krinke]

I have 2 targets, both kernel.org linux-2.6.17.11. Both are currently using rootfile systems from montavista's 2.6.10 distribution. One is a PPC8241 and the other is a PPC8541.
 
On the 8241, I can login with a telnet session as root. On the 8541, I cannot. On both, I can login at the serial terminal as root with no passwd.
 
Neither as a password for root in /etc/passwd. That is, the first line in the passwd file says "root::0:0:root:/root/bin/bash".
 
Being toasters, I dont want a password to cook my toast.
 
The question is:
 
"What are the various things that might cause one toaster to be able to login from a telnet session and another, very similar one to not be able to do this?"
 
Charles