No they don't, most transports are made of plastic, and some cheesy plastic clamping system. If you want a good transport system you have to search for well made ones ...Like the Esoteric Verdes Neo drive is an example of how good a transport can get...there are others too.The goods ones use Aluminum or a combanation of plastic and aluminum. Slot loading means nothing as to the quality of the drive. The best drives I have seen use a drawer. I am not seeing any trend you speak of for slot loaders.