functions, `...' and .Rprofile

I'm experiencing some confusion with the ellipsis argument
(...).

In my .Rprofile, I have the following functions:

   stderr <- function(x, ...) {
     sqrt( var(x, ...) / length(x) )
   }
   se <- stderr

I can use tapply to calculate some means:

   > tapply( Diameter, factor(Region), mean, na.rm=TRUE )

            I         II        III         IV          V
   0.02896429 0.02368421 0.03990476 0.03949315 0.03424021

but, it I try to use my se function, I get an unused argument(s)
error...

   > tapply( Diameter, factor(Region), se, na.rm=TRUE )

   Error in FUN(X[[1]], ...) : unused argument(s) (na.rm ...)

If I use stderr instead, I don't get that error:

   > tapply( Diameter, factor(Region), stderr, na.rm=TRUE )

             I          II         III          IV           V
   0.005167949 0.004405095 0.006588870 0.006633189 0.001857812

I'm curious about what's going on here.  Any ideas?  Is it just
that `...' can only be used in directly defined functions and not
by objects that reference functions?