My bike is mostly Sora, and I definitely can't reach the thumb lever from the drops. For me, it doesn't particularly matter, because I'm never actually in the drops unless I'm going downhill. Your mileage may vary.

ccbloom, I pretty much bought my lower-end bike for that reason. I could have afforded the 105-equipped version (same frame, better wheels), but it's my first road bike, and I couldn't justify the extra expense, and it was More Bike than I wanted at the time.