I wouldn't say that the 'knowing what you're doing' issue as a deciding factor in selecting ThePlanet or Servermatrix. Personally, I believe that as long as you get a dedicated server, you need to know what you are doing or else you be in for the ride of your life.
Servermatrix are the budget entry-level line and ThePlanet is the higher-end professional line. One key advantage of ThePlanet servers are they are higher grade machine with several redundancy add-ons and grants you 100% uptime guarantee and a 2 hours hardware replacement SLA. Servermatrix being a budget line gives you only a 99.9% uptime guarantee and no SLA on replacement but they would replace them as soon as they could.
The Servermatrix plans are basic and those looking for budget servers. If you need a higher end machine with additional features to suit the corporate user than the Planet servers should be your choice.
As with anything budget like Budget Airline, there is always a market to meet the in-between and that's where the Servermatrix servers come into the picture.
No they are different. As the post directly above yours pointed out they have different up time guartentees and SLAs
Another difference between the two is I dont believe server matrix has redudant core switches which the planet does have.