Hello!
You need to make changes in v4.master (in masterpage library), not in default.master.
For details on SharePoint 2010 master pages, please, follow this link:
http://sharepoint-sandbox.com/index.php?/Tips-and-Tricks/Customization/tip-80-sharepoint-2010-new-masterpages.html
Your masterpage trick on my SharePoint Foundation 2010 environment works fine.
Anyway, I don't think, that moving any standard code from placeholder is a good idea. If you want change position of quicklaunch menu, you should move the leftnavbar placeholder itself, including all the contents.
Placeholders are generally used to allow some pages, for example application pages, replace placeholder contents. So, if you hide the placeholder, and move it's contents out, these changes will be lost, and the standard menu will be shown. (and if you do not hide the placeholder, you can get two menus on one page :) )
Hope it helps!