I wonder if sometimes our disappointment at not getting upgraded colors our perceptions. Don't get me wrong. I am as guilty as the next guy about my upgrades. If I'm in a regular room, I'm annoyed.
But truth be told, I am nearly always pre-booked into a suite at Marriott hotels. And I've only been turned down for an upgrade once. I do find that some properties are better than others about upgrading, but for me its been a non-issue. I've even had Marriott properties apologize that the bigger, better suite wasn't available.