Currently, there is a huge effort to made Ubuntu boot faster, but the great issue is what, when Ubuntu - as well as other Linux distros - boots up, it loads many services to support a large variety of hardwares and configurations.
That is convenient for end user what can, for example, easily, connect a printer and work with it immediatelly. BUT, if user have not a printer, Cups, the Linux printer server, will be loaded and stay occupying system memory in vain, because it will never be used. Similarly, if user wants print only one document and save your energy, if he turns on his printer for just do it and turn it off after, Cups will continue in memory.
Multiple problems. How do you detect what the hardware is doing (webcam button, Scanner start) if you don't load drivers?
InetD already is a load-on-demand tool for ports for HTTP, SMTP, etc. It works well to save resources & big binaries from memory, but is slow for intensive-use servers (Apache will outperform it 10x for moderate request counts).