DirectAdmin and Webmin are two completely separate systems. With a base install of cPanel your easily at 512mbs of used ram. I'm running some intense websites and only using 110mbs or ram on my DA machine.
You have to remember, Cpanel includes Spamd as well which uses about 40MB of memory per process. Spamd is not enabled by default on DirectAdmin. DirectAdmin is a little lighter but running the same configuration you should only save about 50mb of RAM from Cpanel to DirectAdmin.
I too love DirectAdmin, but Cpanel really doesn't hog resources, it just includes a lot more. You can disable a lot of features with cpanel and run it on a 256MB VPS if you needed to, it just isn't recommended.
Under decent load it goesn't over 200mb, the maximum i've ever reached is 304mb used ram under sort-of-digg. I run apache 1.3.9 with php 5.2.4 and xcache opcode caching engine + xcache module for wordpress.
All the websites run wordpress (4000uniques/day, no more than 50gb transfer/mo, so not a busy box, but i like to keep things running smoothly).
I've disabled everything not useful, ftp server, spamd, clamd, imap, pop. I've left exim, mysql, apache running.
And yes, directadmin is way leaner in my opinion, i love it. cPanel is overengineered, even if the 11 version is not *that* bad as i remembered.