Hard to Revise a UI

[Nancy Allison]

Hi, everyone. I'm trying to get to grips with a topic that's not clear 
to me. In a nutshell, I'd like to be able to explain why it's a bad idea 
for a company to develop a product's functions first, before thinking 
about the user interface (or documentation).

For example, I know of a startup where the developers have created very 
powerful functions, with the strangest user interface you have ever 
seen. It is just plain bizarre. Functions have strange names; tools are 
scattered around the interface in no discernible order; different 
buttons lead to confusingly similar drop-down lists and directories, 
with no clear indication of what you can or can't do in each area.

It's a geek's paradise, and a total mess. The lead developer said to me, 
"Oh, we'll fix the UI later."

Even in less drastic situations, developers often think this. But, I 
have heard that it may not be possible to completely redo a UI once the 
software architecture is in place. This is what I would like to 
understand, so that I can intelligently explain it, with examples.

So, folks, does anyone on this list know of a good example? Why would it 
be difficult to revise a UI? What are the difficulties involved? Can 
revising a UI actually break the functioning of the software? Can it 
force the redevelopment of the underlying software?  Thanks for any and 
all help!

--Nancy