Investment bankers are masters of Excel, Powerpoint, and Word and they're messing around in one of those all day long. Mostly building financial models and writing or formatting presentations. The work to do is endless, and if it's not the senior members of a team will make something up for you to do.
A huge part of what i-bankers do is pitch - either pitch to a company that you'd like to bring on as a client, or pitch to potential buyers of your client (and variations of that). Junior guys basically make the presentations for those pitches. There's generally horrible project management going on at the senior level as well, and senior team members have no qualms about making you make pointless updates to a presentation (for example, update the numbers in the presentation for the stock price today even though nobody will see the presentation for a week, and you'll have to update it then anyway). In fact, it's sort of part of the deal.
I'm not sure that formula works as well for retailers like Wal-Mart. The nature of wholesale operations is less labor intensive, and the value of wholesale labor can increase greatly with more experience and knowledge like you're talking about. Compare that to Wal-Mart - 10 years of experience isn't likely to make you a much better employee than 1 year.
A huge part of what i-bankers do is pitch - either pitch to a company that you'd like to bring on as a client, or pitch to potential buyers of your client (and variations of that). Junior guys basically make the presentations for those pitches. There's generally horrible project management going on at the senior level as well, and senior team members have no qualms about making you make pointless updates to a presentation (for example, update the numbers in the presentation for the stock price today even though nobody will see the presentation for a week, and you'll have to update it then anyway). In fact, it's sort of part of the deal.