There's a flaw with that logic. Verizon won't have a big enough footprint until late 2013-2014. So, as the Verizon users jump in and out of LTE, they must rely on their slow CDMA (which lacks multitasking).
When an AT&T user leaves the LTE footprint, they can still connect via the HSPA+. HSPA+ is fast and supports multitasking. This will create a seamless experience for the user.