column names in matrix vs. data frame in R 1.8

...

Ok, I'll regard it as an inconsistency that the conversion of

dimnames

to data frame column names changes reserved words to legitimate

names

but direct assignment doesn't.

It's not inconsistent.  data.frame has an argument `check.names' to
control the behaviour on *creating* a data frame, and you didn't

consult

the documentation.  Using the function names<- on the list underlying

the

data frame does not know or care it is applied to a data frame.

After thinking about this, I guess I wonder why names<- shouldn't have
the argument 'check.names' and/or check the class of its main argument.
Why offer protection in one situation and not another?

get("names<-")

After thinking about this, I guess I wonder why names<- shouldn't have
the argument 'check.names' and/or check the class of its main argument.
Why offer protection in one situation and not another?

I don't think you got the point.  names<- applies to a generic vector aka 
list, and the protection applies when generating data frames, not lists.
It really is a feature of data frames, not of lists and not of matrices.

More pedantically,

get("names<-")

function (x, value) 
UseMethod("names<-")
<environment: namespace:base>

so there is no possibility of an extra argument for names<-, even if a 
data-frame method were added.