Maintaining straight and level is exactly the same for IMC conditions as it is for VMC.
On a more basic human factors viewpoint I wouldn't agree with that comment. In VMC what you see outside corresponds reasonably with what your body is feeling, whereas in IMC it can be very very different. Having had "the leans" in IMC I know that it can be hard to ignore the impulse to listen to what your body is telling you is 'clearly happening' and instead just believe the AI and other instruments. Many people who don't have IR currency and have entered IMC inadvertently have come off very badly 'knowing [by feel] that the plane is straight and level' when really it is in a descending turn, but have not believed or reacted enough to the AI and other instruments.
I would recommend that PelicanSquawk goes with an instructor in real IMC and tries various constant rate turns, climbs, descents etc. while at least the AI is obscured from your view to experience these effects.