PaphMadMan, I've also wondered about this (cost of maintaining flower vs resource reabsorption). If you happen to know some experiments where this is compared in orchids, I'd like to know!
In some plants, cost of floral maintenance could be significant:
http://www.pitt.edu/~biohome/Dept/pdf/22.pdf
The trade-off is obviously specific to each species. But for orchid species which keep flowers for a long time, you might be right that the cost of floral maintenance is small.
In addition to the resource cost, there could be a cost in "time", too. Some species seem to shift from flowering phase to next (e.g. growth, rest etc). So cutting flower can change the hormonal balance, and the plant may move on to the next phase in their life history. For example, my P. concolor seems to wait for the end of flower, then it starts to develop the next new growths. P. bellatulum seems to be similar.