I'm in the States (west coast) and in my experience most bartenders shake
martinis, manhattans, anything that goes into a mixing tin. In my opinion it
is typically a case of ignorance, the tender not understanding the reasons for
stirring versus shaking, or speed, ther tender trying to make the drink as
quickly as possible. I can confess to the former as I used to shake all of
these drinks when I started bartending and didn't know any better. I was
interested enough in the craft of bartending to want to learn more about it
and eventually I met people and read things that made me look at shaking
versus stirring in a new way, in an informed way. What I learned is what I
picked up on my own time and with my initiative. For the average tender who
just shows up to work every day and doesn't push their knowledge when they're
off of the clock they aren't likely to discover the differences.
I've written a couple of posts on this forum about why stirring is a better
method for making Manhattans and Martinis (unless otherwise requested by the
guest), here's one:
[Natrone] Re: Technical question on a Manhattan
Check out some of the replies as well, Barmixmaster's for sure.