If I'm not mistaken, that's the clincher with the US.
It's not as easy to get in as it is for most countries.
However, besides working holiday and student visas, once you're in, it's not overly difficult to stay.
We have too many immigrants coming in illegally. We can't take many who come legally - we have quotas for each hemisphere each year, so we let in the ones that we feel will truly benefit our country. It takes so long because we screen everyone that comes in to make sure we aren't letting in felons or crazy people, too lol.
Mainly, it's just the quota. We sometimes fill up and simply have to add people to waiting lists.
America is more difficult to get into because American's tend to be more wary of outsiders as silly as that is, since we are all made up of the other countries when it comes to our ancestry.
I will be honest and agree with some and say we do have a quota. There are a lot of immigrants flowing into the country and so the US is continually screening people coming in in an attempt to control its population.
Given the economy in the US right now they are even harsher because they don't want more competition for jobs.
That is all I can offer you. I do know of a company in NY that hires internationals every summer. Though I don't know about the winter months.