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I would have thought that just having just your own site listed by Google Maps/Local would be a good thing - as you will want people to go to your site rather than to sites such as Internet Yellow Pages sites that may show competitors too.
Are you concerned that a lack of web pages related to your listing may put people off in some way? (or is it something else)
Speaking from the other side of the fence (in that we appear many times in the related web pages on maps/local) I'd say that, as long as you do a good job with content on your site (which sadly, many small/local businesses do not), you should not be concerned that Google is not giving others the opportunity to 'sell' your services for you.
There are instances when links to sites other than actual business can be useful (e.g. genuine reviews or business directories that collect a lot of info on what a business offers) - but these should be reinforcing the message on your website.
What I know is that this is completely selected by Google on the basis of relevancy of the pages related to the business. At times I have seen that some of the webpages listed are from authority site in that business/niche