Yes the Blazers have played 19 games, and nobody else has played more than 17. Could they be mentally fatigued? Sure, that's a lot of games.
But physically fatigued? Who? Let's go through the staring five's minutes: Oden (24) Blake (29) Webster (22) Aldridge (32) Roy (36) Lamarcus and Oden have been in foul trouble half the time, Webster has been in/out of the starting line-up, and Blake is splitting minutes with Miller. Is Roy tired? You could make an argument either way. He's playing less and taking 2 shots fewer/game than last season & he's not going to the basket nearly as much. But he did spend a couple of weeks guarding "bigger" guys at SF - maybe he's still reeling from that - I doubt it.
Also consider the style of play - slowest pace team in the league. If they played Phoenix Suns type basketball, I might buy the tired legs theory. One more thing - they haven't been involved in many close/down to the wire games. They have cruised to several blowout or at least comfortable wins. They don't look tired to me, they look frustrated and maybe a little bored. The schedule is about to get really tough. I have NO IDEA what to expect in December (that 4 game road trip could easily be 4 losses - Orlando, Miami, Dallas, & SA in 5 nights! - 2 back to backs) It could easily be a 4-11 month.