UC is right, the cups are provided as a means of protection for the plant during shipping, and to maintain their supply of water longer while in the store, since most average joes at home depot will kill them by watering with tap and so on... the domes are there to make the plants as user friendly as possible to the stores they are in.
Petflytrap grows it's plants in a large room with grow lights and many many trays of plants, humidity is not as high I think, as many would think, and the plants are usually only domed for a couple of days during shipping... (It's not like they grew up in there!
Ditch the dome unless you have problems... but the domes really don't let the plant spread out and stretch it's traps like it needs to...