The uS education system is very different to the UK one. At university rather than studying your chosen subject for 3 years you major into something. In the first year you will pick a major, (which you are able to change) as in the first two years you basically only have to fulfill your GE's (general education.. which is usually a couple of maths, some language, maybe a bit of science, some writing courses such as english or history etc). Then in your last 2 years you will start to concentrate more on your major. I wouldn't say they aren't to such a high standard... and Harvard I would say is better than Oxbridge. The US ivy league universities are to a very high standard so you shouldn't worry about that.
That is a very slimmed down over-view of unis in the states, i'm sure someone will expand more.
It is also hugely expensive and four years long instead of 3