a previous company i worked for exhibited at multiple macworld expos - and i gotta tell you - the costs are a lot higher than you might expect.
it's not just the huge fee for the booth and the extra staff - these are full-on productions that take weeks of planning and prep. it's also the staff accommodations for those traveling, the lost work time at their primary jobs, the equipment rental, etc.... it's easy to blow millions in a blink.
on top of that, the impression we got from IDG was that their business model of continually rising costs for the exhibitors and conferences etc was never gonna stop. but the IDG value-add is hard to quantify... in fact, i can't think of any company that's made it big solely because of an appearance at a macworld.
from a business perspective - say that you're apple.... you can spend 2 or 3 million (easy) and participate at a macworld - an event at which you might be the namesake but not have control - or spend maybe 20% of that - at most - and get the type of media bang for your buck that we saw with the iPad announcement by renting Yerba Buena Center solo and controlling your message 100%.