If you have to stack your components there are two things to consider.
One is whether the weight will warp any of the moving systems, such as DVD trays or other moving parts which could get damaged if they're bent out of alignment.
More importantly is the heat factor. If I have to stack components I place wooden spacers between them to help create a little circulation. Otherwise you have the heat rising directly into the upper units and this will definitely dry out lubrication and rubber seals or bands prematurely.
If the items are in a constantly air-conditioned room it will help.
Professional video and audio suites with stacked equipment are often kept icy cold to protect the equipment.
I'm a little tight on space for my TV stand...Im putting my TV, VCR, DVD Player and original xbox in it. it is ok if i stack these peripherals on top of each other in the stand. It goes XBOX on top of VCR on top of DVD