I've worked with a number of companies turning over in the low £millions, and it's very rare that the founder is taking lots of money off the table whilst low balling the staff on salaries.
These businesses simply don't have the margins and the runways to let salaries get out of hand.
As most of the economy is made up of these kinds of businesses, many of which have IT as the cost centre providing some non-remarkable CRUD development, this is probably a big factor that holds down average salaries.
Turn it around a little and image you are the small-medium sized business owner. You need a person, but can can only sensibly offer a salary of 75% of the market rate.
Are you best just not to offer the job for fear of exploiting someone or looking like a cheapskate, or do you put it out there and hope to find someone who is happy to work for that price?
[I'm a developer who agrees with the OP so I'm playing devils advocate slightly, but there are two sides to this.]