Yep, I completely agree. We actually did exactly this (just last week) and created a QR for a live demo on our landing page (www.infoduce.com). This way people can see more than just a screenshot before having to "sign up."
Your question in the ease of using QR codes is actually a great question. What many people find is that while it may not be difficult to type a short link, the act of transcribing it from another source is prone to error and mistakes. The value add in regards to technologies such as QR, NFC, bluetooth etc is that it removes human errors.
Don't get me wrong, there are tons of limitations in regards to QR codes as well as other technologies which bridge the gap between the physical and the virtual mediums, but they do serve a specific purpose. At the end of the day, it's really about ROI (very little investment, especially when it comes to QR) and the way they are used.