MT4 uses the Windows default of 96DPI settings, and hopefully it stays that way.
Most users (close to 100% of Windows users) do not change their DPI. If you have a big monitor then less reason to change it, no?
Changing to allow a different DPI will likely open a huge can of worms, especially with object positioning set by EAs, Indicators, and so on.
I sure hope this doesn't change. I have not one, but two big monitors and 96DPI works great!
I'm now using Surface Pro 3 and encountered the same problem.
Managed to find a work around referencing this web site: http://www.danantonielli.com/adobe-app-scaling-on-high-dpi-displays-fix/
Still not ideal but MT4 works much better now.
Hopefully Metaquote will fix this issue for MT4 soon.