Straight Talk is what the industry calls a MVNO, Mobile Virtual Network Operator. They're a company that buys a license to use their phones on the VZW network. So yes, you get partial benefits of the VZW network. However, you don't get the same quality of phones, enhanced products and services, Customer Service, Tech Support or full reliability and coverage of the VZW network.
Sprint does the same thing with Boost Mobile and Virgin Mobile.
So if lesser phones and lesser Customer Service is worth saving money to you, then switch.