The www convention is little more than a side effect of the implementation of the DNS. The convention arose because domain names are typically assigned by IT administrators whose key task is to organize computers according to some taxonomy that makes sense to them — in this case, their function. Hence, machines given the name www were given such because serving Web pages was their job.
This assignment is perfectly reasonable, especially since nobody could have foreseen the explosive growth of the Web, which came into being a great deal later than the DNS.
The label www, however, is particularly laborious to say, adding no less than ten syllables to the spoken form of the URI. If it's disconcerting to witness Internet neophytes struggling to sound the www. in conversation, imagine how they feel.
My official recommendation, therefore, is to make the www-prefixed host name available, but have it redirect to the domain name without the www. Purists may complain at this point that this breaks the domain hierarchy and makes the system harder to manage, but I contend that there are far worse offenders. If it is a serious problem, register your-domain.net and use that for your corporate network, and retain the .com hierarchy for your Web presence and e-mail addresses.