When someone says that, it usually means they don't know how to use command-line programs, so you may want to learn about that.
In the case of the GBA there were a few visualbasic tools that are a nightmare to get working on post XP (more recent, more annoying still) versions of Windows, and even with an XP install you might still have to fiddle quite a bit to get the installers all doing what they need to. VB had thankfully more or less stopped being used by the time the DS hacking scene got going but I will note it never the less.
That said there is merit to the idea that new tools are not as necessary here as a new web browser or new document writer might be in those fields, mainly as a ROM made a decade ago will still have the exact same formats/composition/makeup a decade from now.
I do have a guide to things for the GBA and DS, you might have seen that one already but GBAtemp did have another with a name more closely matching thathttp://www.romhacking.net/forum/index.php?topic=14708
For the most part though things that worked for the NES will also apply to the DS, with obvious exceptions being you will need the relevant emulator, disassembler and a tile editor with support for GBA and DS (they share things but if they are named they will tend to be GBA, things with DS being for the DS) formats.
For the DS you do also have the bonus of a file system being used and many of the formats shared between games (even between different developers/publishers which is pretty rare even on older systems with filesystems of their own) and thus tools to handle them in some capacity. I don't know what we are suggesting for a tool to pull apart DS ROMs right now (I kept on with good old ndstool, which has frontends in the likes of dsbuff and dslazy, but others might go in for crystaltile2, tinke, ndsts or something else).