As to the second part of your question:
A programmer is required to interface with the micro so you can write the code you develop on a PC to the micro for execution.
Some chips, particularly in prototype systems, use a 'drop in' programmer that you physically remove the microcontroller chip from the system and drop into a chip mount on the programmer to write your software to memory, and then replace the chip in the system.
ISP's achieve this without having to remove the chip from the system, usually by reserving a pair of Tx/Rx ports on the controller and requiring the designer to include a small interface plug.
Dev boards come in a variety of flavours. At the most basic end of the scale, bare-bones kits that have appropriate breakouts for a certain chip on an otherwise blank PCB with a hole grid drilled in it.
I think what you're probably looking at is a development kit that has the chip premounted and a set of breakouts and support components already included. Support components may include a typical power supply, a USB controller and interface port, line balancing resistors on I/O channels, etc. In these cases, there's usually a method setup to quickly reprogram the board without having to remove it from everything else (via USB for instance). Some of these boards will even let you run a monitoring host program that executes your code and reports it back to the PC for debugging.
For your project, don't look at ISPs unless you're planning to SMD solder everything but anticipate changes to microcontroller software later (it's the "inflexible" solution). A dev kit is excellent for initial prototyping, but you may be paying for excess functionality that you won't need in your final product (hence "development" board). Barebones kits will give you a decent final prototype to present, but will take the most effort and extra component buy-in to build.
So... Try to strike a balance, I guess?
(sorry for wall of text!)
