In the western world, people without credit or debit cards are such a small portion of the population that this policy of ignoring such users is worthwhile. In developing countries however, there are many services that aim to bridge this gap. I dont know how good they are, or how successful they will be, but people are certainly trying to access this market.

Examples (no affiliations): http://gharpay.in/ - Home cash pickup; https://www.itzcash.com/ - Prepaid Cash card; Mobile Money services in Africa such as M-Pesa - http://en.wikipedia.org/wiki/M-Pesa