I had a conversation with JP and a captain of industry a few weeks ago and asked them the above question. My implication was that it is a good strategy because it fosters trust. It shows that you are confident that the service you provide is competitive. Attempting to lock your customers into your service by making it difficult for them to switch just shows that you are afraid of the competition.
I was hoping for a perspective from the real world - I have never had a customer base that I was afraid of losing. I imagine that a public company that adopted this strategy might face some tough questions from shareholders.
The UK government has legislated to enforce this ability to switch suppliers in industries where it is guilty of creating a private monopoly (i.e. the utilities that my bank helped it sell off in the 1980s). It is a retrospective attempt to correct the skewed market that they created. There is no indication that any of these companies would have adopted this policy themselves.
I know of only one example where a company has publicly said it would help its customers move their business away from them and that is hedged by the proviso that they will only help them move to a competitor with whom they have a reciprocal agreement. The company is Flickr, part of the Yahoo group. Here is Stewart Butterfield's statement, as mentioned in Slashdot and Boing Boing.
The captain of industry I mentioned above said he believed the only worthwhile strategy was to pursue the highest quality service at the lowestpossible price. A somewhat stock answer I'm guessing, but I believe he meant that a deliberate lock-in wasn't a valuable part of a high-level strategy. JP said something gnomic so I won't put words in his mouth. I would be interested in what he and Sean Park had to say on the subject.