Not necessarily, you can curve the sleeve seam to make it smaller or larger over the bicep area:
Whether ModernTailor actually do this or not I'm not sure.
Edited by Sanguis Mortuum - 6/14/12 at 4:19am
You can also give an optional forearm and elbow measurements in the comments of your measurements. For example my measurements say:
looks too long...you have a lot of extra fabric sleeve length wise its bunched up.
X2 the length is way too long man reminds of a time when i used to buy OTR shirts and I would have to buy lengths 34 or 35 to compensate for shoulders and chest muscles etc., but until a tailor measured me i was a true 32inch length and of course when the shirt was built I couldnt believe how well it fit me and how well the shirt moved with me it was an an incredible experience vs OTR.