Re: Abuse, plain and simple.
All my contracts are between my corp and another corp (a go between for the BigCorp I'm consulting for, because in the US no big corporations will contract directly with a little one person corp like mine)
This language covers anyone my corp employs on the contract, which is always just me, but if I had others in my corp it would affect them too. I asked about that clause once long ago, and was told it was a requirement of BigCorp to the go between so there was nothing they could do about it. I've had clauses struck from contracts before, but I only bother with ones that would negatively impact me to a significant degree like noncompetes, and this is one that does not impact me.
Since all of my contracts have been made through contacts in the various BigCorps, who then sole source me to their go between, I'm not beholden to that go between. If I find something I want struck, like the 25% example provided, if they won't play ball I tell my contact. They've always been able to tell the go between to do what I ask. It also allows me to negotiate my rate directly with the contact - the rate that will be paid to the go between. I then tell the go between they can take $10/hr, and if they squawk remind them I arranged the gig, not them, and there are other go betweens available for BigCorp (not always true, different divisions may have set go betweens, but by this time they're scared of me and just accept that I'm probably telling the truth)