There are probably a lot of right (and wrong!) ways to explain this, but the television is designed to default to an 'always on' connection. Starting with the 2009 models, there are two "always on" inputs. One is the tuner, the other is the PC port. Based on those choices, the most obvious common default for most people would be the tuner.

Some regions have a HD tuner, which is not dead, but that can vary by geographical location, and I'm not sure if that's available in your area or if a changeover (recent or past or future) affects that.

There's not an ability that I'm aware of to either disable any ports or change the default port as anything except the tuner.

On that note, Samsung products with Anynet+ should change directly to the input when a Blu-Ray or HT system is powered on, which would avoid having to scroll through inputs. I realize that not all peripherals have or are compatible with Anynet+, but that's the way the units were designed.