No, I don't think that's it, nor do I think it's about him being different than TO. I think it's the nature of the position, that there is some unpredictability. TO had a crap week this week, and had one that is below his skill earlier in the year.
This, and the number of available wide receivers is, IMO, why most leagues play 3 WR positions per team.
I wouldn't be worried about anyone who is producing as well as Smith. If you were right, and he was "on and off" in a pattern, wouldn't you still take him, compared to most of the alternatives? I know I would... if I could have someone I KNEW was going to make me 20-40 points every other week, be sure, he's one of my starters.