Direct Sales means there is personnel (inbound or outbound) selling directly to the customer on behalf of the Vendor.
If you sign up to AWS on your own credit card, there was no inbound or outbound sales motion at all.
AWS's self service motion is extremely efficient for lower tier customers (as the upside is basically infinite as you basically spend $0 to generate N dollars). <- This is also why YC's Request for Startups is mentioning Open Core startups, as the open source offering acts as a loss leader (eg. Kong, Hashicorp, Pulumi eventually)
Traditionally, companies like VMWare didn't support such a model and your only way to purchase was to jump on a call with their account team, but companies are transitioning to that to target low tier sales.