It's a matter of perspective. When I see a newspaper shut down, I don't jump up and down with joy and yell, "Hooray! More room for the bloggers." Sometimes things disappear and get replaced by something better. Other times, things disappear and get replaced by something worse.
When you buy a single-developer program, you essentially buy that one person's quirks and limitations. To take Moneydance as an example, many of its flaws can be traced directly to the fact that it's a single-developer project: the quirky UI, the dearth of keyboard shortcuts, the features that don't work outside the US, the awkward investments interface. To a large extent, its success comes from the Mac world, where Microsoft Money doesn't exist and Quicken development had lagged several times.
I use some single-developer products, but I first take a close look at the developer. I skim the forums. If the guy has a resume online or a Linkedin profile, I read it. It's a confidence-building measure. When I buy a product, I don't usually do it with the intention of making that my one and only version -- I expect to upgrade at some point, and I want to know that the product is headed in the right direction.
One more thing that's unique about Streets and Trips that the other Microsoft consumer programs didn't have: Mappoint. Again, this is both good and bad. Good because the development team isn't totally reliant on the revenue coming in from consumer sales. Bad because it means that the business sales don't necessarily subsidize the consumer product. (In other words, what happened to Autoroute could conceivably happen to S&T.)