Ok, let's recap a bit here, since we're getting somewhat divergent from what's 
actually been said so far.

What I'm contending is that in the most common workstation environment, Linux 
should be able to assume (and check for) a single display, and should be able 
to default applications that have the correct permissions (ie started by the 
user logged in to that display) to display there instead of just failing.

Yes, Linux mostly runs as servers these days.

Yes, there are "thin-client" environments where the local workstation is 
essentially a display for applications running on a central server.  This is 
unusual (in the sense that few of the total installations of Linux are doing 
this), involves different hardware (niether the server nor the workstations 
are configured the way the average desktop is) and most importantly can 
easily be allowed for during configuration.

Yes, there are potential security issues, but if someone can launch an 
arbitrary process on "your" PC, the issue of whether that process displays on 
"your" Xwindow session is relatively trivial.

While we all understand Windows to be inherently flawed, in evolving from the 
single user to the multi user paradigm, they have correctly understood that 
the majority of workstation installations will not have multiple 
_simultaneous_ users.

This assumption that multiple simultaneous users is the norm in a GUI 
workstation environment is something that I feel unnecessarily burdens Linux 
with both bloated code and non-functional default assumptions.

I'm saying that if Linux is installed as a GUI workstation, not a sever, it 
should look for a multi-display environment, and on finding a single display 
in nearly all situations it should default to that display.

I plan to build an audio/video system that will make use of mutiple remote 
displays, but I expect to do a LOT of configuration to make that work, and 
one more step ("yes, this is a multi-display environment") would not bother 
me half as much as programs erroring out because I didn't tell them to use 
the only display available.