They are. funcall(<variable assignment>) is a useful idiom in programming languages where assigment returns (an alias to) the value of the variable, but it is counter-intuitive at first. Even though I have been programming in Perl and curly brace block syntax languages for years, I still find it hard to read -- mostly because when you normally delimit my with braces, you create a new lexical scope. That's what chomp(my $foo = bar) still seems to be, even if I know better and use the idiom frequently.
Not only that, but it is not obvious that the value of $var in chomp(my $var = <$fh>) is being modified at all! After all, assignment, if used in other contexts, returns the value, not a reference to it. my $foo = $bar = 1 doesn't create a reference in $foo, but sets the value of both variables to 1. In fact, I am not sure what the underlying mechanism is. Does it work because assignment returns an alias similar to aliased values in @_ in function calls?
Side-effect free chomp has no similar conceptual problems.