beerslayer, ashServ.exe and aswUpdSv.exe are indeed system services, and as such, can (and ought to) be controlled via the OS's built-in capabilities (namely the Services applet of the Administrative Tools in Control Panel, or, alternatively, by the net start/stop command-line program).
ashDisp.exe is, as you figured out, just the tray icon - if you don't like it, you can kill it... This process is actually responsible for all UI of the resident modules, including the virus alerts, updating windows etc... (the services never display anything, they "don't interact with the desktop" in MS tech parlance).
ashMaiSv.exe is the only exception. It's the mail protection proxy. It's able to work as a service as well, but this is not the case by default.
This process is only needed if you use the mail (SMTP/POP3/IMAP4) proxy. Whether it auto-starts with the OS or not is determined by a check box in the Mail Protection Wizard.
Anyway, I appreciate your care. It seems that you have quite carefully examined avast's workings and your suggestions could make the program better (if you have any specific suggestions/needs/reqs, just tell us)...
Thanks,
Vlk