Rick's (and other's) advice to pack your bag and then walk around your block carrying it (not rolling it!) for an hour or so is good advice .. you might decide you can do without some of the crap you thought "essential."
It is true that Rick's criteria is that you should be able to carry it on your back for long periods. However, why deny yourself of one of mankind's greatest invention, the wheels?
That said, the fewer things you bring, the better. Of course it doesn't matter to people who take packaged European tours that take care of all baggage transfer, from the airport as well as to the hotel rooms at each nightly stop. At hotels, I have seen older couples bringing huge old-style suitcases that made me cringe imagining myself lugging it on a Eurail train or through a city metro.
Still, we have not been able to pare down to one tiny carry-on due to our travel tending to be during cooler or cold periods of the year. Rick also advises people to wash their own clothes and hang in the hotel's bathroom to dry. I'd rather bring enough for a daily change through the trip, and for a 2-3 week trip that adds up quick when one brings warmer clothes. Perhaps we could look for local laundromats, but when in foreign lands that can become a hassle, and takes time from other more leisurely activities. One goes to Europe for a vacation, and not to do laundry! Of course it is not a problem money cannot solve, such as paying hotel laundry charges, or throwing away your dirty clothes (hotels charge more to wash underwear and socks than mine are worth), but it goes against my frugal nature.
More than size, Rick's criteria is about weight: a 20-lb limit. I started to bring my laptop on recent international trips. It lets me look for info while on the road, and has proven useful. However, it quickly convinced me to get a smaller and lighter unit. But my just-purchased 13.3" laptop still weights 4.4lbs, without its power pack. An excuse to get a netbook? Economic stimulus, anyone?
Gee, all this talk about travel makes me itching to go. I may need to get off this forum to go look for travel deals.