Omae,
I agree on the paragraph saying what you said but that does not really help with table variance and how GM's would rule do to str, Bod and race. In fact the paragraph does not really even talk about stats or race in any way it just says be reasonable. Which can mean a lot of different things to different GM's and players.
I tried to pick an extreme example to show how much trouble it could have, but I also like your pixies with assault riffles.
MDC
See, this is where the other side of the problem comes in that many companies are trying to avoid

Now, not only do you want a straight STR+BOD = X carry weight, you now want them to factor in the mass of the race in question.... This is not a paragraph or two and a simple chart... this is a paragraph PER race AND a chart which works out to probably a page, maybe two. And while that may not sound like much, if it already costs the copy/customer an average of $0.25 a page, it adds up. (Arrived at by taking my purchase price of SG at $59.99/231 pages, Run faster purchase price $59.99/253 pages, Run and Gun $69.99/213 pages. Averaged out)
And that doesn't include the said headaches that would entail from all the whining and crying some customers would do over the fact that their Pixie can NEVER move more then a bowling ball because of the body/str/size of a pixie, or that the Troll can bench press a car -one handed, because of the same rules.
now, believe it or not, I am not picking on you (Go look up my 'Pixie with Guns: with picture!' post in character creation from a year ago, You'll see that I am sort of on your side here!), And my table has sat down and house ruled out some basic carry weights for characters due to mass and size. (We are all Industrial construction workers, so we see EVERYTHING in terms of numbers and weights, so its a given at our table) We even have rules for harnesses and combat webbing! Because we are anal. We just don't need it printed in a book and charged to us when WE probably have a better idea of the tolerances of strength, mass and the human body then the writers do seeing as we live this stuff everyday, 12 hours a day, 26 days a month. (We industrial construction workers are some of the most 'practical S-M-R-T people' you can meet... Even the Iron-head with they walnut sized brains (with swelling).
For example I stand 6 feet tall, weigh 180 lbs. I am 42 years old and NOT particularly muscular. I drink. I smoke. I would say my SR stats are STR 3 and BOD 3. Which in SR terms I can carry 30KG of gear with out effort.
Now, lets look at what I actually DID (in real life) today....
I set up Stanton lighting on the very top of and FAS stack, the Stanton light weighs 65 pounds. The stack is 8 stories high (88 feet), which means I need to wear fall arrest gear which weighs at 47 pounds for the harness, hardhat, lanyard, beam-buddy, and shock absorber. To actually hook up the light to the base I require 5 tools for a total weight of 30 pounds. And that's on top of all the extra clothing I need to wear, as this is an ACTIVE SMELTER! (Fire proof level 6 - heat reflective one piece jumper 45 pounds. emergency oxygen mask and tank 18 pounds)
total weight: 205Lbs. OR 93Kg.
And since I did that eight times in twelve hours, I would say I wasn't overly Stressed.
So... by SR standards I am either Augmented or drugged out to the Gils. A well built Troll, Or their numbers are WAY off... As what I did for an average day would take a strength of 9 in the SR world..
Now, the reason I can do my job is that the total weight of everything but the light is even dispersed over my total body thanks to a series of webbing and strapping. It's the Stanton light (only) that is a pain in the ass, awkward and tiring to carry.
This all just gets too complex to write out in a simple little paragraph or two, and invites arguments when presented.... Hence why most companies just say "YO! GM! You deal with it as you see fit!".
Is it "Passing the Buck" or "Deferring to a Superior Opinion and Judgement" ? That's up to you to decide.