Re: In a nutshell
"Pre-sales people" are just that - people who work on a project before the customer has placed an order or the contract is won.
Sales people in small IT businesses are expected to be sales-orientated technical people. They may have shared access to technical experts on an ad-hoc basis.
However, winning a large contracts involves more than meeting-and-greeting, drawing up a two or three page proposal and closing the deal - there can be a raft of technical consultancy, architecture planning, system specification, BOM/BOQ/proposal generation, installation-costing, licensing negotiation, support agreement negotiation, training services negotiation and graphic design/presentation work - largely undertaken by qualified professionals. These are the "pre-sales people". Their work is often wasted if the company does not win the order.
There are, of course, post-sales people who can do all this stuff as well - but they're too busy delivering projects HPE already won.