You only need to buy it at the airport if you want a Welcome Suica. You can buy a regular Suica at any station with a multi-function machine.
The only real differences between the Welcome Suica and a regular one are the 500 yen deposit (Welcome Suica doesn't require a deposit) and the limited validity (Welcome Suica automatically expires after about a month).
The only real differences between the Welcome Suica and a regular one are the 500 yen deposit (Welcome Suica doesn't require a deposit) and the limited validity (Welcome Suica automatically expires after about a month).