"Pro" when it comes to hardware refers almost as much to the service and support infrastructure that backs it as it does to the hardware itself.
A Dell server is unremarkable in most ways and very expensive.
The reason to buy it is that for every server that Dell sells, they guarantee to keep replacement components for it on the shelf for the duration of the warranty and/or support contract. Those parts gather dust on the shelf for years in most cases and then are recycled.
What it means is that when your Dell Pro server or workstation goes down, you have anywhere between guaranteed 24-hour depot return-to-service and guaranteed 4-hour onsite return to service.
Dell literally drives to your site, with the part, and gets you back working within 4 business hours.
Meanwhile, gaming companies and fruit companies are slapping the "Pro" moniker on all manner of high-margin sparklies these days.
Imagine if a real enterprise had deployed these, only to find out that when they break the employees using them (and the projects dependent on them) stand to lose weeks of productivity.
Insane.