The problem with that model in many software markets is that the proven value of the bazaar development model means that when you do that, eventually one of the purchasers of the binary is going to make the code public (because the GPL means they can), and once they do that, the cat's out of the bag, and people (both users and alternate service vendors) can roll their own binaries), commoditizing the software and reducing (likely, eliminating) your ability to charge for binaries rather than ancillary services like support and custom development.
It's a bit sticky, because the GPL doesn't allow any constraint on distribution. However, the argument intellectually is that you're not stopping distribution you are merely refusing to deliver the "service" due to a breach of the service agreement - "I'm not stopping you distribute, I'm saying if you distribute then I won't be providing this separate service X".
Here's a 2014 example from a RedHat APAC service agreement:
"Distributing the Software or any portion of the Subscription Services to a third party or using any of the Subscription Services for the benefit of a third party is a material breach of the Agreement even though the open source licenses applicable to individual software packages may give you the right to distribute those packages (and this Appendix is not intended to interfere with your rights under those individual licenses)"
Where:
"Software” means Red Hat Enterprise Linux, JBoss Enterprise Middleware and other software programs branded by Red Hat, its Affiliates and/or third parties including all modifications, additions or further enhancements delivered by Red Hat.
URL: http://jp.redhat.com/licenses/apac_enterprise_agreement_appe...
There aren't many megacorps that would pay you loads to customise a code search engine.
But don't the receivers of the source then have the same right to redistribute it without charging?
It doesn't have to be initially, but once you redistribute it to others with the permission to redistribute it that defines Free Software, the probability that you end up competing with gratis derivatives of the same code base tends to unity over time.
So, Free-for-a-price software really relies on a premium price charged to early users (often only the first user); IOW, its more like selling bespoke software development services than like selling other software licenses.
Nobody in the comments mentioned the most successful case: Cygnus Solutions had been developing the GNU Compiler Collection (GCC) for good money, all under the GNU GPL. Notably, they made a lot of cash from a deal with Sony to support the original Playstation in gcc.
A good read about how they marketed Free Software on John Gilmore's pages: http://www.toad.com/gnu/cygnus/