Whenever I see a theme that utilizes footer encryption, I simply find another one.
I'd say the majority of other people do it as well.
There is no legal necessity to maintain footer links, since they're considered a modification of Wordpress code, which is released under the GNU General Public License. So, no theme creator or vendor can force any user to keep any links in-tact. If they decide to take it a step further and try and prevent a user from removing them, they're going to lose business and won't get backlinks anyway - since most just find a new theme, or go out and purchase one.