You seem to measure difficulty differently then many of us do. If a game is longer with content instead of fluff it is better. Your argument that some "long" games are padded. Some games don't even need to exist. You are making a case against some games instead of long games.
Witcher 1 & 2, Fallout 1,2, Vegas, More then half the FFs,(FFI, FFIV, FFVI, FFX being my favorites) Fire Emblem series, KOTOR 1&2, DA:O, TES series, Arcanum, Divine Divinity, BG series 1 & 2, PS:T, Persona series, The World Ends With You, Golden Sun, DQ series, Shining Force, Dues Ex, Super Mario RPG, FFT.
These are all games I wouldn't mind buying for full price (most of them I did)
Now notice a pattern? Yeah, time sinks and ones I deeply enjoyed. People want bang for their buck.
CoD? Waste of time and the single player, doesn't even need to be there.
Most arcade games? Dull games that rely more on reflexes then thinking.