I noticed that new ST3 does not use visual styles on Windows.
While 3125 contained an embedded manifest with
Microsoft.Windows.Common-Controls reference, 3127 and higher do not have it. However, despite of new theming feature, there are some system dialogs which depend on ComCtrl32.dll and who look weird on Windows 7 without it, such as "Save Changes?" message box, "Open File" and so on.
Of course, manifest can be added as external file named
sublime_text.exe.manifest, but it still requires a
comctl32.dll import presence to enable visual styles, which can be done only by modifying ST's import, which, for sure, brokes a digital signature of ST.
MSDN says that:
Prior to Windows 8, you must specifically configure your application to use visual styles; otherwise, the application's common controls are always rendered[...]
So, it seems, only Windows 7 users need such manifest.