I strongly agree that Microsoft should let users override the regional settings. This is not just to allow users to use the formats they like but also to allow users to correct the mistakes that Microsoft makes in the regional settings. For example, Microsoft has never got the Philippine regional settings right. I reported this to Microsoft several times. In Windows, setting the region to Philippines would set the measurement system to imperial even though the Philippines follows the metric system. At least in Windows, that could be corrected via a control panel dialog box. In Windows Mobile, that could be corrected via a registry setting. But in Windows Phone, we're stuck with the mistake.
Similarly, in Microsoft Office, setting the language to "English (Philippines)" would cause the spelling checker to use the British dictionary even though the English used in the Philippines is US English. The workaround is to just set the language to "English (US)".
When I did the online Windows 8 upgrade, I was shocked to find out that my old US English Windows version was upgraded to a British English Windows 8. Fortunately, Windows 8 allows users to change the language. But if I reset the Windows installation, it would revert to British English. Then I would have to change the language to US English again.