Having a reseller account means you have less to worry about since you don't own the server. You're just leasing space and bandwidth. So if any hardware problems do arise, you won't have to pay to fix them. It's the responsibility of the server owner, in this case, your web host, to get it fixed and ensure maximum uptime otherwise you have the choice of moving to a more reliable host.
In order to own a server, you'll either need to buy or rent one. Either way, it will cost a hell of a lot more and if you don't have too many resold accounts, it would be difficult for you to make a profit at the end of each billing cycle.