People have already seen the demise of MSFT's Zune products, RIMM's Playbook, etc. If I'm going to choose between an iPad or a Surface, and they are the same price, will I really gamble on the Surface when I know it might not be around 1 year from now? I know the iPad will be around. I can't say the same about the Surface, and if it's gone quickly, then I will kick myself for not buying an iPad.
This is something that the Amazon Kindle Fire did right. They priced it low enough so that there isn't as much risk, and their Kindle brand makes me believe it will be around for a while.