I’m sure there are web sites that you can search which give you a full overview.
It is my understanding that group policies through an employer do not exclude pre-existing conditions, and individual policies only exclude pre-existing conditions for a set period of time.
I was diagnosed with a curable cancer in 2008 and am presently receiving follow-up care and scans. If I lose my job, I have COBRA coverage available and any future job with a group health insurance plan will cover my medical care. It appears that the one difficult thing would be starting my own one-man company or small business. Other than that, I should be able to have care if I or my wife have a job with a company that offers a health plan.
The thinking is.. if these conditions are being treated regularly, the regular treatment outweighs the risk of a catastrophic medical event occurring from these conditions. It makes sense to not cover the conditions if they have not been treated for a truly significant amount of time (i.e. >1 year) because it is probably statistically significant that a major claim will be made to the company for the condition that has not been treated satisfactorily. However, upon reading the fine print of my policy, pre-existing conditions are only not covered for a period of 6 months, after 6 months they are covered.