My growing conditions are exceedingly dry, with very little humidity in the air. I was quite surprised to discover that Phalaenopsis orchids do just fine, in fact are one of my more successful houseplants.
They regularly send out some aerial roots. I don't think they're trying to absorb water, there's none to be had in this air. I think it's more part of the plant's natural search for a secure anchor. It doesn't really "know" that it's in a pot, it came from a very long line of epiphytic ancestors.
I enjoy seeing the aerial roots, and wouldn't dream of cutting them off. They are green, and add some photosynthesis capability. Plus, any time you make a cut you are opening a wound that is susceptible to bacterial, fungal, or viral infection.
The only times I've seen excessive aerial roots is when the roots in the pot are in trouble, also just above an area of stem rot. They are a symptom of the problem, not a cause.
Try browsing a bit in the "Root Porn!!" section of the Advanced Discussion forum, lots and lots of amazing pictures of aerial roots.
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