we could support 40, our existing 2 engineers are basically under-worked - we have 2 because it would be insanely irresponsible to have just 1, aside from company ownership (which is able to do the work also, if needed). if we absolutely had to, we could cut that down to 1 full time guy. let that sink in; 1 full time guy to manage 40 customers.
having said that, we're still growing as a business, because we've embraced the new reality, but it hasn't been without turnover and pain. we're also putting money into developing products.
the kicker is, even with the R+D, we're more profitable now than 5 years ago, with LESS ops folks (ostensibly less people to do the actual work, though we all know that's not what's really happening). i imagine the same exact thing is playing out with larger in-house staff, as you describe.
this is the new model. WAY more output from less but higher paid full time people, small networks of high-$ specialized consultants, and smaller firms and IT groups working in mercenary fashion. embrace it, or you will bleed yourself dry in less time than you think.