Yes, I have heard that activity on Twitter is like going to a party ..ask questions ..be engaging ..etc. Yes, you are right, this should form the majority of one's activity on Twitter.
However, once you are good at this, and so have happily confirmed your non-a##hole status amongst your followers i.e. as a friendly, supportive, communicative chap, then who amongst them would resent the occasional promotional tweet or, say, an invite to a webinar or a link to a blog post. Very very few and those that find intrusive/offensive can just unfollow.
By the way, the Belcher guy is Perry Belcher not Peter Belcher.
Best Regards