The leak occurs because customers/ potential customers will frequently recall the name of the site and add ‘.com’ almost instinctively, unless they recall that it is on a relatively unusual extension .net, .org etc.
Inevitably, the more the [non .com extension] site is marketed, the more traffic is sent to the .com, however, the problem is that the .com domain may well resolve to a competing business’s website.
Some businesses are willing to live with that loss (perhaps because the [non .com extension] is a relevant, memorable generic, for example) – for them the [non .com extension] is a viable option.
However, without a compelling reason like the one mentioned above, I would argue that a business on a limited budget just cannot afford to develop a site using a [non .com extension] domain name. It is as simple as that."
SOURCE: http://www.domaining.org.uk/2007/12/10/spectacular-net-or-a-...
HACKER NEWS THREAD FOR ABOVE LINK: http://news.ycombinator.com/item?id=4108016