Looking at the web environment, it is quite good for a bootstrapped startup. Reasons are:
Are there any other business areas that you can see that have the same or similar characteristics that provide the same opportunities as the web for a bootstrapped startup?
I would say that a home inspection business, telemarketing business and the like are low barrier businesses since they require nothing but human resources. These businesses can also be started with a single person but they don't scale well.
I would like to comment that for web startups, it is because of all of the things that you mentioned, low barrier to entry, low startup costs, etc... that web startups have a hard time differentiating from everybody else and reaching success.
It is hard to come up with valid differences or advantages to help you succeed in this crazy competitive area (the lower the entry barrier, the more competitive it is), perhaps concentrating in vertical markets and find opportunities for new businesses in those markets is a better idea.