Yes, that was an inartfully constructed sentence. No, consultancies are not like "rent-a-centers". The fallacy here is that the fundamental unit of commerce here is "talent/hour". Here's a sampling of all the things that have value in these transactions:
* An hour of talent
* A committed hour of talent a week from now
* A committed hour of talent a year from now
* Any number of commited hours of talent from the same person
* An hour of talent on 1 month's notice
* An hour of talent on 1 day's notice
* An hour of talent from a problem domain specialist
* An hour of talent from someone intimately familiar with your company's business processes
* Hours of talent rotated through a small group of people to keep them fresh, at less than 3x the cost of a single person
* Total scheduling flexibility over talent/hours
* A candidate for internal career development (management, architecture, etc)
* An A-player who poses no political threat to the company's org chart
Some of these are benefits of full-time employees and some of them are benefits of contractors. Some are benefits of staff-aug contracts and some are benefits of project-based consulting and some are benefits of transactional one-shot consulting/advisory gigs. It's naive to suggest that only a raw hour of exercised talent is worth money.