I think this depends on the direction and importance of the communication. It some cases you will have two way communication that will require typical request/response transports(HTTP, etc.). In some cases you'll be able to use one way communication. This would open you up to using a messaging transport, and supplying the ability to move some processing "offline". This could help you scale the site, but you may just move your problems somewhere else without some careful design.
Importance matters because if you have some information from the user you don't want to lose, say orders, then that may also push you towards something more durable like messaging. You don't necessarily need a Service Bus to use one way, durable communication, but the feature set provided may make things easier.