Wow! Those are some healthy looking dendrobiums. Some types of orchid flowers have problems adapting to their new homes - it doesn't necessarily have anything at all to do with anything you might have done. My mom bought me a dend once that was in bloom with many buds as well. It was a cool rainy afternoon and she carried it home - a walk that probably took 15-20 minutes (sometimes much shorter periods than this can have the same effect). This little cold "blast" made ALL the flowers and buds drop in a few days.
The next bloom cycle, where it was on the seasonal blooming cycle for my geographical area, it did fantastic and stayed in bloom for three months. Most orchids will do MUCH better keeping their blooms when they develop and bloom in the places where you are going to show them. I have found that giving them good air circulation goes a long way in helping the blooms stay. Keep out of cold drafts. Good luck and enjoy your plants! Very nice.