I would say this is true the bigger the hotel the easier it is for them to give a online broker a screaming deal and let them fill the hotel up in larger volumes.
With any smaller 50-60 rooms or less I would say you get a better deal by contacting the hotel direct. You are usually dealing with the owner or manager atleast directly and they are on the pulse as to what they have free and what they can offer.
For example a large website will list a price and it maybe be a good price but they dont really sway from it day to day or week to week. While a smaller place by contacting the owner will see whats free and coming up and if its a open slot will gladly give you a deal instead of just leving a empty room sit.
So I guess it depends on what type of hotel experience you are after.