agree, what is meant?
sound? or structure?
bit of personal experience. when i was young i used to listen to a lot of electronic music, and fortunately some classic techno as well, which seemed (and seems) really loopy for me. when i first got to a techno party in the uk (2002) it was bit of a shock for me as the sound was completely different to what i was thinking techno restricts to. e.g. i was bit surprised to see dj doing nothing while it sounded like he was torturing his knobs and faders. and the sound i heard was rich.
in other terms, i was surprised with "progressiveness" of techno.
since then i quite regularly go through new releases, started buying some and so on. but i can't say i noticed it getting more progressive - it changes and develops, but both now and 5 years ago you could find a lot of loopy stuff as well as compound-structured "songs".