Hi Resourcey,
Hopefully I can help... I live in the US and am now an American citizen but I was in your position previously.
Let's start with EIN's and SSN's... they are both forms of a TIN - Taxpayer Identification Number.
EIN's (Employer Identification Number) are used for companies, Not For Profits etc. - basically, any person or organisation that employs other people.
SSN is the Social Security Number of an indvidual. If that indivual runs a company that is effectively a sole trader or partnership that doesn't employ anyone in the USA then the SSN can be used to identify that entity too.
For those not resident in or citizens of the US the TIN is actually an ITIN (Individual Taxpayer Identification Number). It's often confused with a SSN because it is exactly the same format. But it begins with a '9' and that indicates that the ITIN cannot be used for employment in the USA.
Does the IRS insist that you have a ITIN? No. But then whoever is paying you the money has to deduct witholding tax from it and account to the IRS for that money. It's a real pain to do this so I can only assume that Apple (quite sensibly IMHO) choose not to by insisting that all submitters do have a TIN.
You can see how to apply for an ITIN at
http://www.irs.gov/businesses/small/international/article/0,,id=96696,00.html
You can find help on applying form outside of the US at
http://www.irs.gov/businesses/small/international/article/0,,id=96690,00.html
I hope this helps....
Best wishes.... Ian