Third party devs don't make lots of games specifically for portable consoles, look at the Nintendo 3DS and Playstation Vita as examples. They're going to continue plugging along making the games they make regardless of what the Switch does. That's perfectly fine, because Nintendo hasnt relied on third party devs since the SNES. Sometimes they succeed, sometimes they fail, but they ultimately do based upon what they create, not what outsiders do.
The home console peripherals are not substantially impacting the build materials for this device, and removing that portion makes the marketing muddied for the device. It's way easier to show the Switch on a big screen and then removed from its dock to convey the quality and depth of the games you're going to get on the device.
The $300 price point is based upon what Nintendo thinks they can make on it in the launch year, not how much it costs to make (it's basically a Shield Tablet, which retails for $200 with a bigger higher quality screen). It also gives them the latitude to drop the price later this year or early next year and potentially lose the dock further down the line.
It's also bulkier and less portable than an iPad Mini, so it's not exactly a great replacement to the 3DS. It's backpack, train, plane, and bus portable, not pocket portable.
The way Nintendo could really get momentum is by turning the Nintendo Switch into the place to play first party games (something the Vita lacked) and indie games. Offer indie devs a waiver of the licensing fees on the first ~50,000 units pushed and do weekly promotions on the front page of their shop. While Xbox/PS4 is plastered with nothing but Battlefield/COD/Destiny, Nintendo highlights Stardew Valley/Firewatch/The Witness/Inside.
Maybe it's just my age, but I'd buy a switch for those games. I'd rather play those kinds of games on the Switch than on the Xbox or PS4, and those are the level of games that Ubi, EA, and Activision would be willing to port over. Games that are already primed and prepped to run on a system of the Switch's capabilities.
EDIT: I guess what I'm saying is that you don't have to remove the home console portion of the device to emphasize the portability, or reduce the price. They can emphasize the portability with the dock included, and they can reduce the price when that is appropriate. It's not appropriate at launch to make the device appealing to everyone, because they probably don't have the units available to fulfill those orders. $300 now, bundles at the end of the year, and $250 next year and they can maximize their revenue without stripping the console down.
