It's hard to give any advice at all based on your post, but you're correct that the necessary software doesn't run on the Mac.
The decision to make a significant investment in Macs for a business is going to depend on a lot of things, not the least of which is how big the business is and what your business does.
If you're an accounting firm to whom QuickBooks is your core app, switching would be insane. If you're a small graphical design studio with no tech support staff and you only need one accounting computer to run QuickBooks, you'd probably be far better off buying a single PC for that specialized use and Macs for the rest of the computers. If you're a smallish office that never uses anything but a web browser and Word on all the machines but a couple in accounting, then it's possible switching some of the computers to Macs could be a profitable choice, but it'd have to be considered carefully.
Think of it like this from a business perspective:
What apps are vitally important on what computers? If there's no Mac version, you'll need a PC for at least that workstation.
How big/good is your IT department? If the answer is "tiny" or "none", considering Macs might be wise on account of the reduced IT overhead.
How big a task would the switch be? If everything is ingraned Windows-only, it's going to be a lot more expensive and time consuming than a startup buying their first set of hardware, or a company converting from something ancient that's going to require new software and training anyway.
Does the Mac actually get you anything? Are there specifically better apps available, does the generally lower TCO specifically apply to your company, or is switching going to cost more in confusion and new software than it'll gain in security and better hardware/software?