Hardware is ... HARD. A lot harder than software. There are no nice frameworks assuring your board works or that you aren't paying five times the cost on your plastic parts because of poor mold design. Iterations take months not days. This isn't something you can bootstrap with 4 people, the first plane ticket to China to meet with contract manufacturers is going to cost more than the entire server running a web app for 2 months. The container shipping it back will cost more than the food two founders eat a web company in a year.

BUT - at the end of the day you have a real product, which people will expect to pay for, and a barrier to entry behind you.