does Visual Studio 2010 not have a "join lines" keyboard shortcut?

This is not exactly what you want, but I find it useful nonetheless.

If you are at the end of the first line, press Ctrl+Del to join the next line and delete any white space between them.

You still have to be at the end of the line, but this will work on virtually every editor, without any modifications.

I use the CodeMaid extension for this, it provides a Ctrl + M Ctrl + J shortcut to join lines (and some other useful things too)