Same goes for tank without gasoline, bolters without magazines, lasguns without powerpacks, etc. I think daemonic engines are surely a sign of technological advancement. The warp energy is just their power source. Vraks 3 mentioned that many of the daemon engines were recent appearances, which implies that Chaos advances their technology just as the Imperium does.
I think the two sides are about even in technological advancement. Whereas the ignorance of the Imperium prevents great advancement, the fervent fanatiscm to their gods cause (Change, war, indulgence, or disease) limits them to making machines only for thos purposes. And the new Imperial Guard codex makes mention that many of the vehicles are recent additions to Imperial inventories. The Space Marines also have a history of adapting technology (Razorbacks and Land Raider Helios are good examples.)