Over the past few years the definition of Evangelical has changed considerably I think as there are churches who state they are but are not.
These findings are very sad. And you're right, the definition of who is and who isn't an evangelical Christian has changed over the years. Rob Bell, Jen Hatmaker and Andy Stanley still call themselves Evangelicals.
This is, of course, not to say that there needs to be a more concerted effort from pastors and teachers to ensure church members are taught the main doctrines of Christianity. Perhaps surveys like this can be used to spur believers to study Scripture and to be able to articulate to others what it truly means to be a Christian.