"The reason why they chose ExtJS of Sencha instead of Backbone/Ember/Angular is due to the level of support they can get from Sencha, not because of any X number of features."

I would pay 10x more for consulting instead of support. The constant need for support means your team is incompetent. If you need external support to keep things moving, chances are you won't get very far.

"in the eyes of the 'business guy' they'd opt to throw money at the problem for it to go away, no time should spent troubleshooting or googling."

I'm also a co-founder and technical guy, I assure you spending money is always the last thing any company wants to do.

"Decisions like that don't come from developers, they come from the typical 'business guy'."

Lead engineers are usually who de-facto make those choices together with a CTO.

"To sum it up: your client can't rely on a community of people that supports things only in their spare time."

I've been running an 'enterprise' company with Rails, for almost 7 years now. Both the applications and the company are large. I don't really understand what 'rely on a community' means here. Who does not depend on open source software?