Marathon + Agility did NOT protect you from IEDs. In addition, IEDs deserved a nerf. Rather than keeping the balanced equipment ie claymores and betties, they decided to combine them into one all-powerful package. If something like an IED has two great abilities, there has to be a large enough counter balance in order to make them more fair. With the way IEDs were prior to the patch, the balance of the IED was offset.
Granted there are counters like Sitrep and Blast Shield, but the IEDs made those perks too essential rather than simply helpful. If I wanted to avoid betties and claymores, sure I could equip Sitrep/Engineer, but I didn't need them to save my life every time. Now IEDs...they're a different story.
~RUGGED SAVIOR