Deflecting Arrows would be hard
Imagine a 1st level Fighter who took Deflect Arrows and is armed with a one-handed weapon and no shield (thus one hand is free).
Now imagine that 1st level Fighter is up against 3 Orc soldiers who happen to be henchmen of a 20th level Ranger (a hypothical exaggeration). This 20th level Ranger is a master with a bow, but because he took other Feats does not have Shot-on-the-Run.
The 3 Orcs are on three sides of the 1st level Fighter, two of them flanking.
The 20th level Ranger is within 30' of the 1st level Fighter and he somehow has had the True Strike spell placed upon his first attack against the Fighter. This 20th level Ranger also does not have Improved Precise Shot (he took other Feats), and the 3 Orcs and the 1st level Fighter keep moving enough that the Fighter normally recieves cover from at least one of the Orcs. Thus, the 20th level Ranger finds it necessary to move more than a 5' step and only takes one shot per round.
The 1st level Fighter is not flat footed and is aware of the 20th level Ranger.
Under the rules for Deflect Arrows, the 1st level Fighter can defend against the 3 Orcs (two of them are also flanking him), make his own attack, AND ALWAYS deflect the one arrow shot by the 20th level Ranger, regardless of how high the Ranger's attack roll is; even if that attack roll is boosted to +40 and the Fighter forgot his armor and has no DEX bonus whatsoever (AC 10).
Now this is a purely hypothetical situation and not likely to happen; the situation is just a demonstration of a possibility, not a probability, and to me shows that Deflect Arrows in the RAW is too black and white to be balanced in 3.5e.
So in my group, we do opposed attack rolls.