Employee
Back in my publishing days we used to try to distinguish between the type of "appliance" you point out and purpose-built hardware by calling software shipping on off-the-shelf-hardware "softpliances". I agree, there is very little difference between shipping software and shipping software installed on off-the-shelf-hardware with the exception of eliminating installation tasks from the deployment.
Deploying these "softpliances" is more about ease of installation and rarely has additional benefits aside from perhaps the ability of the vendor to harden the underlying operating system - a task many customers don't have time/desire/skill sets to perform.
As far as performance goes, there's no advantage to a "softpliance" versus software deployed on customer provided hardware. The gains come when you move to a true purpose-built hardware platform, which is a completely different ballgame and may not be applicable to all types of software.
Good point there, thanks!!
Lori