in reply to Re^2: Shouldn't references be readonly?
in thread Shouldn't LITERAL references be readonly? (updated)

That seems to be because a reference to a literal actually constructs a new scalar; note that the examples you gave where an error was thrown at an attempt to modify a read-only value did not involve references, but only aliases to literal values. I suspect that the anonymous scalar you get when you say \1 is probably modifiable. There is no such thing as a literal aggregate in Perl — the {} and [] operators are defined as constructors instead.