Q: When people in the investment business charge a fee based on account size, rather than commissions based on transactions, is it just another way to pay for the same service?
A: YES & NO. First, the answer is often yes, because there are many more registered brokers in the U.S. than there are registered investment advisors, and therein lies the difference: When a broker charges a fee (see their fine print) they are charging you "in lieu of commissions." So in this case it does mean the fee is just another way to pay your broker. This approach has two important features, one good and one not good. The good is that it eliminates the incentive for the broker to be a promoter of transactions (churning). The bad is that many investors become confused, hence your question, and wrongly think the fee is for advice or management, when it absolutely is not. It is very important to remember that if you are doing business with someone who is functioning as a broker, rather than as an investment advisor/manager, then they are regulated under the law as a salesperson.
The answer to your question becomes an emphatic no, however, if you are dealing with a representative of a Registered Investment Advisor (RIA). In this case the fee is not in lieu of commissions, rather, it is a management/advice fee that compensates for a variety of professional services, none of which is compensation for selling securities or advocating transactions. This approach has several important features, and it is likely that you will like all of them: Personal and objective investment advice, a relationship with an investment professional rather than a professional salesperson, higher level reporting including performance reports, and a commonality of purpose, meaning your advisor and you want the same thing -- to see your assets grow (as opposed to asset "turn-over.") And finally you will be dealing with a licensed person who is paid for advice rather than activity. Interestingly, brokers often charge "in lieu of commissions" fees at rates that are as much, or more, than those charged by a legitimate advisor.
The first question you should ask anyone in the investment business is on the subject of experience and qualifications. The second is: Do you function as a broker (a salesperson, regardless of how they are paid), or do you function as a fiduciary? (a RIA representative). Only then will you know what you are paying for. Do you wish this subject were less confusing? Call your legislative representative and tell them the current rules and procedures are failing to alert the public as to "who is who."