Nononesense and Electric Savant,
there is a simple answer why different people get different deals. First, it depends on the account size that you bring to the table. Second, the volume you trade per month (although you can negotiate a deal without min. volume). Third, your specific requirement (for example, which markets you trade. It all comes down to customization and your needs. Of course, the downside is that an ill-informed trader will not ask for the best deal and therefore pay more than he could have paid with a bit more negotiation skills.
Obviously, you guys love IB (as can be seen in all threads here). We all accept that and I also like IB for many of its features. But other traders have a need to trade more than one single contract a trade (you previously admitted your trading size freely). Additionally, some traders might trade Eurex and are not willing to pay 4.8 RT at IB. As the commission on many contracts traded on Eurex are way lower than the ones of most e-mini contracts it would not make sense to pay 4.80 which would basically pay for guys like you!!! In fact, you guys should be required to pay 6 bucks or the like for your low volume. So, it makes sense you stay with IB. But try to understand other peoples' needs. AND Nononesense: No, no one in this thread does need API connectivity to X-Trader (although its offered). But we will all contact you and ask to share your wisdom if the need arises. (Gosh, why does this guy come up with his API stuff in every single thread although commissions are being discussed? Must be a very agressive salesguy: What front end for IB did you code? sorry, I forgot).
*** Note: I am not affiliated with TT, Patsystems, Global Futures, Adv. Futures, Velocity, and any other broker or system provider.