You can on a website with HTML 5 specify exactly the font and how it should be interpreted. Those look exactly the same. Good. But if they are not use then often some old font names are used with no more info than size. If nothing specified then browser default font is used. But what about anti-aliasing and handling the hinting? It is about trick the eye to think something is very round when it in reality it built based on squared pixels. Microsoft Truetype was a must when you made the transition from CRT screens to LCD screens. I have seen websites were the text makes the column wider, into the need row and messing up the whole websites layout due to this. I think what it all comes down is that Microsoft old fonts are therefore still used a lot. On Android it is all okey due to we have such high DPI screens.

Yes, over the last years fonts have improved a lot, making the Desktop look good.