Standard parts are available right away, only not-so-common parts have long leadtimes.
You CAN buy most right away for double the price, if you like.
It's the same for all companies, they all have to plan ahead like that.
Of course, something like Apple is different. If they want to buy billions of part from you but only if they are available within a certain time frame, you'd try everything to make that happen - even giving smaller companies longer lead times if need be.
If it's anything like the aluminum extrusion industry (I work in the IT Department of an aluminum extrusion company), then when a big client orders something it gets scheduled as early as possible, and will delay orders from smaller clients. If a smaller client orders something, it is scheduled when it can be fit in, and is more subject to change. It doesn't even really matter about the size of the particular order, only the annual order amount. That is, if a company that orders $1 million worth of extrusions a year orders something, they will get priority over a company that orders $1 hundred thousand a year, regardless of the size of their current order.