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Lack of standardization: Mac OS is a BSD UNIX under the hood. Lots of Open Source Software and the standards that come with it right there. And a single image of Mac OS can be applied to any hardware the OS supports without driver problems. Nice and easy to standardize your image.
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Inability to roll out Group Policy:
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Cost of Macs during computer refresh:
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Audits: I worked in a company where compliance audits were the norm. Kicking out a Mac report was no problem. Kicking out a Windows report was no problem. As long as you implement the systems needed life is good.
Standardization: What does this even mean? A single OS X image can be applied to all supported hardware platforms with no driver issues. That’s rather standardized. OS X is a BSD UNIX under the hood, with lots of Open Source Software implementing various RFC standards.
Group Policy: Trying to manage an OS X computer like you would a Windows computer is going to be as successful as managing a Linux computer like you would a Windows computer. Why is this an issue?
Cost: Apple’s hardware has a different depreciation rate than Dell, Lenovo, HP, whatever. Personally I don’t think there is an overly logical reason for it, but that’s the case. Used Macs can be sold for more money than a used PC purchased at the same time. Your accounting should be factoring that in. I’ve done enough laptop roll outs to know that once you step up to vPro and other related technologies that let you fully manage the hardware lifecycle, acquisition cost of Mac and PC is a wash.
Audits: Again, this is a managing OS X like you would Windows issue. I had no problem getting the needed evidence and maintaining compliance of the OS X computers when audited for HIPAA, SOX, PCI, etc. In some ways, Macs have a slight advantage here. You can show your auditors the Group Policy being applied to your Windows fleet.
Can you prove those settings are actually being applied to a Windows computer? (If not, you should learn how before an auditor asks.) On the Mac side, the compliance reporting comes from collecting inventory and configuration from the Mac directly. So instead of showing “here’s Group Policy” it’s “Here’s the policies we’ve pushed out to the Macs. Here’s the collected inventory of the random sample Macs you selected proving compliance.”
Seriously, pull this off and the windows guys will hate you because now the auditor will ask them for the same evidence. Poor lazy bum Windows admins. 
Managing Macs is a great place to cut your teeth on empowering the end user, encouraging self service and self reliance, and driving down support tickets and support cost on a platform. Learn to do it, then come full circle and apply that knowledge to the Windows, Linux, whatever side of your house. To borrow a phrase, Different is good.