I can't help it if you can't conceive of doing anything the least bit different from the way they did things in the 1940's, no matter how inefficient it is.
The cost to build the mobile launch platform for the SLS is about $300 million dollars. Even through the project was started for Bush's Ares program, it won't be completed till 2016, and just the modifications from the Ares configuration are budgeted for 1000 man years
of design and construction work. That gives you the ability to launch a rocket every few weeks, at maximum, because each rocket has to be assembled in the VAB, loaded onto the mobile platform, rolled out, and then sat on the pad for a few days.
If the SLS flies 45 times, the mobile launch platform alone adds $10 million to the cost of each launch, or about two million dollars per seat. There's no engineering breakthrough that's going to lower the cost of a steel tower
by some factor of three, so cheap space flight cannot ever happen as long as you use a big giant tower for the launch. And that's not even figuring in the VAB, which would have a replacement cost somewhere in the $5 to $10 billion dollar range, and which eats up over a hundred million a year.
When space flight advocates talk about a future with $100 a pound to orbit, or even $10 a pound, you can't keep using a launch tower if it alone is adding more cost than that. Even if the rockets were free, the cost of maintaining the support equipment required for the vertical launches keeps the price per launch hardly better than buying an airliner, using it once, and throwing it away.
And if there's an explosion on the pad, which could certainly happen, the entire sytem will be grounded for the several years it will take to build a new tower. As in-depth NASA studies found, the tower will not in any way survive a pad explosion. Not surprisingly, they found the most likely cause of a pad explosion was a collision with the launch tower, which became a major worry with the Ares design. Of course you could build several towers for redundancy, but then you've spent over a billion dollars.
We got to this point because the early small rockets are trivially easy to raise, and when the space race started in earnest we just threw money at the problem. The Russians didn't build and transport their Soyuz vertically because they couldn't afford to, whereas we could afford to do almost anything. SpaceX took a page from the Russians and became the only US launch provider that doesn't build their rockets vertically, just standing them up prior to launch, and not coincidentally is by far the lowest cost provider.
If they were extremely confident in their engine start, they could lift the nose up with just 30 SuperDracos, and they're already going to use eight of those in the Dragon capsule just as abort engines. They don't need to do that because their rocket is small enough to raise vertically right at the launch pad, but as rockets get bigger that operation becomes much more difficult and expensive, and eventually impractical.
So, a question: How many Orion capsule abort motors would it take to raise the entire SLS to vertical while its fully fueled? About six. If you use twelve you could lift the entire rocket, including the SRBs, and flip it vertically in the air. The abort motor is the tiny little thing on top of the stack. Lifting and fipping are infinitely easier than getting such a vehicle to go supersonic, and then getting it all the way to outer space.