How important is it to install on the program files folder?

In a proper installation of an average software, its executables would be in the program files folder; its user data in the user's application data folder; it's non user specific data in the all users application data folder; and it should usually be able to run under non-administrative privileges. These guidelines could easily be ignored on XP, but they are an issue on Vista and 7 due to UAC.

We're on the verge of releasing a major version of our software. It's a CMS, used by our clients as their main work tool, and their IT staff are well familiar with it. If we want to be fully compatible with Windows 7, we have to make quite a few changes, and we're already on a tight schedule.

Question is: we can easily have our clients install our software outside of program files, or have them run it as administrators. I think it's wrong, but I need some ammunition: why should we install on program files, with all the limitations that come with it?

EDIT:

1. I'm asking this here because I'd like to get IT guys input. For programmers input I can just ask the guys next to me instead of stackoverflow. This is NOT a programming question.
2. I'm asking this because we'd like to make our software better. Old installation habits go back about 15 years, when the software was first created. Fixing its installation is a matter of priorities, nothing else. Worse comes to worse, it'll be postponed to the next version.

Technically: Yes.

Logically: No

Business wise: I know a lot of companies that would throw you out based on obvious quality issues. Even if you do not certify for windows, you should not blatantly violate common sense and guidelines.

I personally would return the software as faulty and bill you for every minute we spent with it - due to gross neglect.

Someone on your end obviously messed up and never read how to program windows. Happy fixing ;)

So, at the end: It is going to cost you. ESPECIALLY in a CMS area - highly competitive.

You should read ALL of the following reference material before making your decision. It's a lot, but then you wanted to write Windows apps so...

Windows User Experience Interaction Guidelines

Windows 7 and Windows Server 2008 R2 Application Quality Cookbook (Windows)

Certification requirements for Windows 8 desktop apps