on Gates's custom

Daily TelegraphがBill Gatesにインタビューをしました。世界中でかなり読まれている記事です。どうぞ，各自で全文に目を通してください。ちなみに冒頭の部分の2カ所ほど，Othelloくん，解説をお願いします。

Bill Gates has frugal tastes. Asked to name his luxuries, he lists DVDs, books and takeaway burgers. It is hard, however, to think that any fast-food outlet would get rich on Gates’s custom. During a long list of engagements beginning well before dawn, he consumes nothing but cans of diet cola.
For America’s wealthiest citizen, austerity is relative. The retinue of staff and the private jet hint at a fortune said to be approaching £40 billion. As he told pupils at a south London school he visited this week: “If I hadn’t given my money away, I’d have had more than anyone else on the planet. Ninety-nine per cent of it will go.”
http://www.telegraph.co.uk/technology/bill-gates/9041726/Bill-Gates-I-wrote-Steve-Jobs-a-letter-as-he-was-dying.-He-kept-it-by-his-bed.html