The problems in a lot of IT shops are that instead of training people to troubleshoot Dells (or HP, or Lenovo, or Apple), getting them the diagnostics, spare parts and warranty procedures for a few models, and site licensing software for one architecture, you now have to get people to troubleshoot fifty different kind of hardware, drivers, antivirus, patches, license all the software for Mac / Windows / Linux etc. It's certainly doable, and in some environments there's certainly a business case for it, but it means multiplying the size of the support staff, which costs a lot of money -- or putting up with the kind of ad-hoc support that existed before standard PXE boot images, in-stock spares, test-to-work standard hardware/OS/applications.