Who would maintain such information repositories and what would the incentive be to take that on? (As they no longer could be supported by ad revenue.)
>>hanspe+(OP)
Resellers maintain such information. There are many websites where you can specify the weight, height and hundreds of other parameters for your product search.
>>hanspe+(OP)
Ad revenue is not the only kind of revenue. Traditionally, people would pay purveyors for goods or services they deemed valuable enough to acquire/use.