I think that chaining the lights is not because a ceiling might not hold the weight, but more to do with if there was a fire, you wouldn't want the lights falling on the fire fighters. Rules for luminaire support are in Section 30-302. As far as chaining, mabey this is an Ontario building code?
All fixtures in a drop ceiling must be chained. Whether they are fluorescent, exit lights or pot lights. This is in the Ontario electrical code. The only other alternative I am aware of to NOT have to chain fixtures is to have stamped and approved ceiling drawings from an engineer that shows the drop ceiling was designed to handle the weight placed upon it.