I think that as a host you have an obligation to make sure that you are aware of how your pets are behaving and whether the guests are OK with it. In the case of dogs being allowed on the couch, for instance, I think that it would be sensible to tell your guest that. Lots of people don't allow dogs on the furniture.
Even if your guest is fine with having a dog on the couch with them, it's useful for them to know whether it is OK for them to encourage or allow this. Plus, if you tell them up front that the dog is allowed on the couch it gives them the option to sit on a chair instead, if they would prefer not to have the dog sitting on on near them.
I think also it's important to remember that not everyone who visits your home will be as comfortable with your pets as you are, or as familiar with what is or isn't appropriate in terms of addressing any behaviour - and that someone who is not very comfortable with that type of animal is much more likely to 'overreact' (e.g. swiping a cat which has 'attacked' them, even if they were startled rather than hurt).
Because of this, I do think that the onus is on the pet owner to be very clear and to be very alert. As a guest, it can be very awkward to say "Your cat/dog is bothering me"
I like dogs that I know - I would not be comfortable with even a small dog which I wasn't familiar with sitting on the couch next to me - if your (generic you) dog is allowed on he couch and you would not want me to put him gently on the floor if he jumps up by me, then you need to tell me that before I sit down, so I can sit somewhere else.
When I had my cat I would warn people that the right hand end of the sofa was 'his' seat - he preferred it if I sat there and he sat on me, but if you sat there, it was very likely that he would come and stand on or next to you, complaining that you weren't me. If that was not something he guest was comfortable with they can sit elsewhere. If I didn't warn hem, I would not then think it unreasonable if someone reacted badly to having him jump on them or shout in their ear - it's my fault , for not warning them, not theirs for reacting.