David,
Let me add on to you what you said, it's not entirely accurate.
RCLI was re-branded with the release of vSphere, VMware went "v" crazy and pretty much renamed all their toolkits/SDKs/etc. The new name for RCLI is the vCLI which is just a set of canned Perl scripts that provide much of the same capabilities as the familiar "esxcfg-" commands that were found in the classic Service Console on ESX, in fact all the vCLI scripts have the same name as the esxcfg- commands (e.g. esxcfg-vswitch / vicfg-vswitch). The main reason the RCLI/vCLI was created as David mentioned was to fill a gap in automation and management with ESXi, since the Service Console no longer exists. To provide a familiar scripting experience, the RCLI/vCLI was available to help automate, configure and manage your ESX and ESXi host.
The vCLI as mentioned are just a bunch of Perl scripts, the scripts themselves actually utilized the what's known as the vSphere SDK for Perl, a Perl binding to the vSphere API, which is what it ends up talking to. The are other SDK's including PowerCLI which are just Powershell bindings to the vSphere API, VI Java for Java users, etc,etc.
So what does vCLI and vMA have to do with each other and how are they different? Well for one, vMA was also re-branded back from VI 3.5 days, it used to be known as "VIMA". VIMA/vMA is a VMware virtual appliance that runs on RHEL5, it's purpose is to provide an environment that is similar to that of the Service Console for classic ESX, in which you can write and run scripts for centralizing your management for your ESX, ESXi and vCenter hosts. Within the appliance, you have a pretty stripped down RHEL5 installation but it also includes the vCLI installation in which you have access to all the vCLI scripts + vSphere SDK for Perl in which is basically required for vCLI and also includes a bunch of other utilities. There's also 2 additional utilities vi-fastpass and vi-logger that's not found any where else and these are some pretty nifty tools, to find out more, check out the vMA documentation.
So now having said all that, you can see that vMA encompasses vCLI and there are values added by using the vMA appliance. The biggest thing for new users is that by using vMA, you don't need to install vCLI on another remote system whether that be (Linux, Solaris, Windows), you upload the OVF and you can get started right away!
The vCLI + vSphere SDK for Perl utilities provide quite a bit of canned scripts for your automation, but for more advanced things, you probably will need to write your own custom scripts, many users aren't aware of this and think the limitation of the vCLI are just within those scripts, they're not. Depending on your comfort level, you may combine the existing scripts are write new ones to fit your needs. Here is a collection of the vSphere SDK for Perl scripts I've written and shared with the community and majority if not all support running 100% on vMA -
Here are few additional resources of my own that can help you get started with the vCLI and vMA along with the official VMware documentation of course as they provide lots of examples
Hopefully this clears up any confusion 
=========================================================================
William Lam
VMware vExpert 2009
VMware ESX/ESXi scripts and resources at:
VMware Code Central - Scripts/Sample code for Developers and Administrators
If you find this information useful, please award points for "correct" or "helpful".