Those are all standard company line responses.. Any Bridgestone tire with a G designation, such as G701 or G852, are specific orginal equipment originally designed for a specific motorcycles. The G701 is the standard front tire for the Honda Valkyrie and maybe Goldwing of some years. The G852 is designed for the Suzuki M109. I assume, due to our sue-happy society, Bridgestone is not about to say that a tire designed specifically for the Suzuki M109 will work with any other bike.
Triumph is contracted with Metzeler for the Rocket, so of course they are not going to recommend any other tire.
The Avon Cobras in our size are not standard on any bike, so they can recommend them.
I have recently mounted the Bridgestone Exedra Max on the rear and the Bridgestone G701 on the front. Now, the G701 is "only" rated to 130 MPH, but since I've rarely hit over that speed in 64K+ miles, I have no problem using that tire. So far, I am very happy with them. And they are hugely less expensive than the Metz's or Avons.
I've went through 3 sets of Metzelers, 3 sets of Avons, and now the Bridgestones. I love the Avons, but seeing the price saving on the Bridgestones, I thought I would try a pair..
So far, so good.. Although, I've only had them for a couple hundred miles.