What is the difference in Cisco routers at the enterprise-scale?

Armed with CCNA, I am about to jump into the corporate world and, while reviewing the profiles of Network Engineers on Linked I came across their work ex statements like " Configuration and troubleshooting of Cisco 2500, 2600, 3000, 6500, 7500, 7200 Series routers. "

So, it will be great if someone from the corporate world could elucidate if there is major difference in these router series or like iPhone they just have minor updates with every other series.

Thanks in advance.