Your observation is correct. Frankly, many probably will agree that creating a new framework from scratch is not easy. On top of that, very likely you need to create a tool (or customize one) to support the framework to work efficiently. Speaking for myself (have done work in RWebSpec, TestWise and BuildWise), it is not easy and cannot be done in a short time. Check out this article,
http://www.wired.com/2013/04/linkedin-software-revolution/, if LinkedIn need to lure someone from Google to implement, very few companies can.
So, what does that ("jobs asking creating a framework form scratch") mean then? In my opinion, it is a sign that lack of understanding of Test Automation, and it is common. Some companies look for and wish for a magic sliver bullet. In fact, frameworks are already there: Selenium-WebDriver + RSpec. It is how to use them. From my experience, test automation is not that hard, it is simply very easy to get it wrong (like your recent posts, trust me, a lot more challenges when you have more test cases to maintain everyday). As I said in 'Practical Web Test Automation' book, the most efficient and economic way to seek help from experienced test automation coaches (look like LinkedIn did, and Facebook somehow get Simon Stewart, WebDriver lead, from Google as well).
I have started working on a new book: "Web Test Automation Clarified", to answer some confusion over test automation.
Zhimin