Jelle:
I wouldn't call the pages generated by DNN "massive" but that is just my opinion. I crunched some numbers on page sizes, etc. for the main page of some sites. As you can see below, the CollegeParkJudo site is only 13KB, that in my opinion is not a heavy page, with compression it goes down to 5KB that needs to go over the wire.
microsoft.com
Original size: 40979 bytes
Size if compressed: 8769 bytes
Transfer speed improvement: 4.6 X
dotnetnuke.com
Original size: 73257 bytes
Size if compressed: 14832 bytes
Transfer speed improvement: 4.9 X
collegeparkjudo.org
Original size: 12609 bytes
Compressed Size: 5357 bytes
Transfer speed improvement: 2.3 X
The thing with compression is that it just works, no need to mess with anything else. Because of the nature of ASP.Net, not necessarily DNN, there are areas that out of your control. But, if the site performs well (specially with 4.4.1) why bother with HTML optimization, which is a pain to maintain. I rather go for simplicity of maintenance but that is just me.
Carlos