When I first started into the hosting business, I like many others started with a reseller. I stayed with reseller accounts at first, I had 3 of them. It made more sense to upgrade to a VPS, and then a dedicated server. I suppose I used the resellers for the first 2 or 3 months, then went to the VPS for a month or 2 and then on to a dedi.
That was with my first hosting business. With my current host, I started out again with a reseller, but wanted complete control, so I went to a dedi after only a month or 2. I am not using much of the server at all, and the load / speed seems to keep the clients happy.
But, just because 1 host upgrades in 3 months doesn't mean you should. Be sure you have plenty of income / clients to be worth getting a dedi server.