About a quarter of the time, I have a vendor briefing and I never get any contact information from the people I talk to. It's not a huge deal, because if I have a later question I can always go to the vendor web site and call the main phone number or send an e-mail to firstname.lastname@example.org, but it's not optimal.
First, it's an extra step or two, so if I have a general question that several vendors can answer I'm inclined to call someone whose number I have. Second--a somewhat embarrassing admission--I don't always know who I talked to. At the briefing, we get on the phone--sometimes several people are on cellphones without great reception--and the PR person says, "And here is Sam Xyzertizhw to talk about WhizBang's great new product." No title is offered, I'm not quite sure if I got the name right, and it turns out I didn't when I try to follow up: "May I please speak to Sam Xyzertizhw?" "We don't have anyone by that name here." "OK, how about a Sam in Marketing?" "No, I'm sorry, sir." "Hmm, OK, thanks, for your help."
PR folks often don't give that information out because they want to be the conduit between the analyst and their client. By interjecting themselves in the middle, they can prove their worth: "I scheduled six analyst briefings and handled four analyst calls this month." However, the turnover in PR firms is notorious, both in terms of personnel and clients, so often the PR person you talked to six months ago is either gone or no longer handles the vendor you talked to.
So, if you're a vendor and you want to make it easy for an analyst you briefed to call you, put your name and contact info in the presentation and then make sure you send me the presentation. It's a simple thing, but a lot of vendors don't do it. Be one who does.