I think this is the crucial point. Probably the people who clean hotels do not usually buy Roombas. If a lawyer buys a Roomba, they are saving time that is worth 100/hour (or whatever). If a hotel buys a Roomba, they are saving time worth 10/hour (or whatever). A very different calculation.
At the same time, even if you assume the lawyer could spend his vacuuming time working instead (not exactly a safe assumption, as I learned the hard way once) the hotel laborer easily spends more than 10x the amount of time vacuuming that the lawyer does.
