I don't think personal taste (desire to stand on middle of unlit bridge) is necessarrly the issue.
This puzzle is similar in structure to others which involve a river crossing and a boat. With that situation, leaving someone off half-way would not be recognized as a good solution! Anyone who has experianced *that* puzzle may be trapped in that mode of thought.
This actually makes the bridge crossing an interesting test. It identifies how closely the candidate reads and (truly) understands the question (without reguard to prior experiance). It also tests the understanding of limits (as used in calculus).
My one gripe with the solution is that in order to approach the 17 minute solution, the individual groups end up standing closer and closer together until they are substantially walking across as a single group. The true solution would end up reducing to 10 minutes in this case (speed of slowest walker as all cross together). Makes me wonder if there isn't a missing requirement to the puzzle such as the (rope) bridge being unable to support more than two people at one time. This change would force us to re-evaluate the proposed solution.
T