Rails3 question about why using the older style :controller option breaks under the following scenario...

I'll probably do a bad job at describing this but I'm going to give it
a shot (pretty new to Rails)...

In my main application layout file I have the following link in my
menu bar which works just fine:

<%= link_to "Meters", meters_path %>

I originally had it as the following, since I had copied from some
older rails2 project:

<%= link_to "Meters", :controller => 'meters' %>

This latter link is working fine on most pages BUT when I implemented
Devise into my application and I tried to go the 'edit user' screen
which goes to the user/edit view, I end up with the edit user page not
displaying due to the following error:

No route matches {:controller=>"devise/meters"}

It's not really a problem since using the newer restful approach of
<%= link_to "Meters", meters_path %> has things working, but I'm just
trying to understand Rails better and why using the older <%= link_to
"Meters", :controller => 'meters' %> no longer works correctly on the
User pages (it's fine on the other pages.)

I'm guessing it has something to do with the fact that the user edit
form is mapped to {:action=>"edit",
:controller=>"devise/registrations"} and maybe that somehow forces the
whole context of the page to think it's 'under' devise directory?
Being new, I'm a bit confused what's going on so any help appreciated.