The DSi didn't spell the end of the DS, the GBC didn't knock the GB out and the N3DS won't kill the 3DS. It provides a performance improvement, that's all - the exclusive titles are there to entice you to upgrade.
Now that's something I disagree, DSi came to replace DS Lite, as DS Lite came to replace DS Phat.
There were still games that supported DS Phat when DSi was released, but DS Phat was not been manufactured anymore.
Probably, the current 3DS will stop been manufactured as the new 3DS dominates the market.