Endoman - sorry I have no specifics for you, but evrything (even the bikes, all bikes) have maximum weight guidances (I think its 32 stone for the entire bike!). The rack will have, or have had, a sticker with a max of 10 kg/22lbs; all luggage (Givi stuff, for example - their e21's have a max of 5kg!) is the same, with ludicrously low figures given.
The good news is that everybody regularly exceeds the over-cautious guidance weights without consequence.
Its more important to get the weight distribution correct imho
What it all means in a legal sense, I've nee bloody idea, though!
One thing I would add (and sorry to add to your annoyance, endoman, but feel I have to say it) is that occasionally, some pieces of Suzuki luggage
can sometimes open when it shouldn't, apparently...Someone with more experience (as opposed to my zero!) of the luggage may be able to tell you more, and how to ensure it doesn't happen to you.
I must stress - its just the odd item...