A lot of the web hosts I Come across are resellers. This is understandable, but is it possible to find out who they are reselling for? Also, is it possible find out who the registrar of a domain is? I know of whois, but it doesn't seem to tell me the original host/registrar.
Nerdie is right - and no matter what - whether they are a reseller or they own their own data center (the two extremes) make sure to always maintain your own off-server backups even if your provider says they do it for you. Trust me - if the worst ever does happen you will be very thankful you've followed this advice.
As for finding out who the root provider is, there are many ways to do it - checking the SWIP information on the IP address itself is often useful if they are hosting their site in the same location as their customers but if they aren't it won't help you.
Also, as for who registered the domain itself - that won't make much difference in most cases.