The real question is what is Apple going to use the server farm for?
Beating a few benchmarks on performance, price or power-consumption is usually a good way to break into, or return to, a market.
Apple also has a rabid user base who will gobble up anything they put out.
If we say the cash cost to them is about half of that, I think 500 mil can be recouped selling their services to about 50 or so large corporations and governments.
Apple has cash to burn and it needs another business leg to hedge against its consumer offerings. 500 mil in R&D and insurance sounds about right. We will have to wait to hear what they tell their shareholders, in any event.
EDIT: They are definitely not going to invest 1B to earn 46 million over 10 years. 46M will not even cover executive compensation for the same period.