I like these extra features. It's fun, like discovering a pocket you didn't know you had in a garment you've worn for years. Still, I wonder sometimes if Perl's casual observers are put off by these things. My guess is that it depends on one's attitude. Some are (as I am) delighted by discovering something new in something old. Others may be dismayed that they did not know the language as well as they thought and may even despair that they'll never master it as they'd like.
I don't recall the last time I ever "discovered" a feature in a function I use in perl, as you described the default to $_ above. Rather, I go about things the opposite way (if you could call that). I use the internal functions the way I'd expect them to, and I'm pleasantly surprised when they allow me to use them that way.
This is probably what leads to people thinking perl is hard to read, as you alluded to. My personal opinion on the matter is that people are trying to read perl without taking into consideration the style of the individual programmer. My feeling is that's the reader's fault, not the programmer.
But this is why we have the little "+" and "-" buttons.