I intended to not start my first post with negativity. But Neal, the quality (or lack thereof) of the songs you've posted, and content of your posts, in general, really don't compliment the intellectual conversation that is happening in this thread, and that's a shame. There's always that one person who is super stubborn and doesn't really "get it". It really hurts the thread. Lastly, if "writing a good melody" is "easy" for you, either your definition of "easy" is very different than most, or your standards of "great" are extremely low (and after hearing the songs, I'll side with the latter).
To get back on topic, the word that intrigued me most about the original post was the word "memorable". I think "memorable" is a subjective characteristic, but I also think it can be defined and established in all of us at a very early age (through nature, not nurture). I was thinking about this a few months/years ago...
The songs that will be most successful within the mainstream market are the songs that are most "memorable" to the largest majority. As a writer, diagnosing and re-creating those melodies and intervals is the hard part. Doing it repeatedly, is even harder. Doing it repeatedly over 15+ years, is even harder (Max). I think all of us, at the early stages of brain, speech and sound development, learn to associate certain noises, speech inflections, modulations, volumes, etc. with certain feelings. I truly believe that the intervals that a particular person is most drawn-to can be traced back to this period, as these are the very first audio and noise associations we are introduced to when we were born. Hell, when we were kids, maybe the opening theme song of the most popular cartoon at that time is the reason why we like the pop music we do now (and maybe the most effective pop songs now, use the same melodic intervals as those particular theme songs). Maybe the melodic intervals/notes I hit when I say "Do you want a snack?" to a little kid, over and over and over again, are the intervals that he will grow-up loving in music when he's in high school. I also believe tastes/preferences can evolve, much in the same way they're developed.
Max has figured out a formula that has transcended a number of generations, across a number of musical genres. For all we know, maybe he is listening to speech patterns, 90s sitcom theme songs, police sirens, and other general noises found in every day life and literally implementing them in his songs (knowing every human is familiar with those intervals). Who knows. But I truly believe he has figured out something the rest of us have not...and it's much deeper than just on a musical level, in my opinion. Finding out the root, and core, of what makes something "memorable", is a good place to start, in my opinion...
Also, I co-manage a relatively new songwriting duo out of L.A. who is very influenced by Max/Luke, and have written with Savan, as well as many other established writers (Kara Dioguardi, Lauren Kristie, etc). Here is some of the stuff -
http://soundcloud.com/blueprintmusicprod/up-all-night/s-4MhzIhttp://soundcloud.com/blueprintmusicprod/timeless-cmoncmoncmon/s-KPMsOhttp://soundcloud.com/blueprintmusicprod/champagne/s-IVowQhttp://soundcloud.com/blueprintmusicprod/freefallin/s-SVTVP