Hi egodestruct,
In some cases yes but it would depend on the materials and the reasons for the impression and on the effect they have in terms of PPP for a specific person. In general terms though it would probably be fair to say yes. For example it could allow a softer latex or other foam material to stay more consistent across the surface for longer periods of time and it could also prevent the wool from shifting or showing deep impressions but all impressions in a mattress are not necessarily a “bad” thing … only if they are deep enough to affect you in terms of PPP. It also depends on whether the impressions come from the breakdown of a material or whether they are part of the normal response of a material. Thicker layers of wool for example will generally compress by about 30% of it’s height over time and this is part of the normal response of thicker layers of wool on top of a mattress or a wool topper. In this case body impressions aren’t an indication that the mattress is breaking down or is defective or uncomfortable and is part of how wool layers conform to a body shape. Deeper impressions in foam materials on the other hand are usually undesirable and go hand in hand with foam softening and past a certain point can indicate that the foam is breaking down.
I certainly understand and this is part of the tradeoff that can go with an online purchase vs a local purchase and is one of the factors that are part of each person’s personal value equation and risk tolerance. It’s also why I generally suggest that a local purchase that has a premium in the range of about 20% or so (depending on the person) vs an online purchase would be roughly equivalent in terms of “value” assuming all the other pros and cons are the same and you are making apples to apples comparisons.
In some cases the return privileges of an online purchase can also be an important factor as well … at least for peace of mind 
Phoenix