I still think its disappointing, as the only thing Welbeck brings IMO is a high work rate, pace we have in Walcott (and Oxo and Sanchez when fit), but I don't think his touch or end product is up there with the other players I mentioned. I guess Wenger will be looking for Ozil, Santi and Giroud to create/score an early goal and then press/harass Spurs all over the pitch from there - something Welbeck is very good at.
Or (as this is Arsenal) Walcott is carrying a 'slight knock' which will keep him out for the next decade...
I'm not surprised to see Wellbeck, if he is fit I would have started him ahead of Walcott as well, remember as I said before a midfield with Walcott-Ozil is too lightweight in terms of keeping that defensive discipline. Wellbeck in terms of work rate and his defensive duties is better suited than Walcott, and I think that's one of the main reasons he is starting ahead of Walcott.
We have more than enough attacking options already on the pitch, Giroud, Cazorla, Ozil, Ramsey, Wellbeck. Walcott can come on after in the second half if needed.
I guess by selecting Welbeck, Wenger is going to look to close down the opposition and hit them on the break, allowing Spurs to have most of the ball.