I've had my table break in the past from a very large client.
Although I never ask weight before I see a client. My current table can handle static weight of 1000 lbs.
However there are some tables that handle half that in static weight and a little less in working weight. So I can understand why some may inquire.
That being said, it really shouldn't be necessary to ask, as most good tables are affordable and are capable of holding plenty of weight.