I don't know why they're considered disposable - i think it's totally wastefull! I have a bunch of the same brand's little bowls with lids that I bought ages ago for Marshall's frozen baby food at daycare ... he still uses them for his snacks! I guess it's the same thing as those ziplok "disposable" plastic containers - they say they're to be tossed, but I really think they're fine to keep - and much cheaper than the "permanent" versions!
The straw cups don't really leak that much - I mean, like I said earlier, don't give him grape juice in it and then send him toddling to the living room, but for the high chair, they're totally fine!
Kate