Having been in the ink business for a number of years in the early years of inkjet printing, it's been interesting reading all of the above comments dissing dye inks. I will not argue, that dye inks are not at all as fade resistant as modern pigmented inks, but not all dye inks, or pigmented inks are the same either!
Dyes came into inkjet printing initially because they required much less maintenance in operation compared to pigmented inks. Just look at the appearance of the cleaning stations of pigmented printers, compared to dye printers. after a year of use. Pigmented printers have a lot of pigment residue built up, compared to dye printers. It's only been the last 15 years or so, that the engineering of pigmented printers has advanced to the point that they are as reliable as dye printers in terms of head clogs, etc.
In terms of print life, a good set of dye inks printed on a good swellable polymer coated paper, should deliver pretty decent print life (20-40 years) depending of display conditions including good atmospherick conditions. Your modern Epson and Canon pigmented prints seem to be coming in at the 80-100 year life. HP prints are about double that at 200 years. (These are all generalized figures) But why, do you ask, do HP prints seem to last so much longer? Better pigments? My hunch is, yes, slightly better matched pigments, but also their use of neutral gray printing inks and a lot of gray component replacement in the prints. Where Epson uses a lot of Lt Cyan and Lt Magenta ink in their printing algorithms, HP uses a lot of Light gray and gray inks. This also results in a much more neutral looking HP print. This is also why Epson printers are always doing nozzel checks to make sure their prints look right.
Getting back print life, Dye inks are susceptible to dye interactions. Not all dyes sets play together well. Pigments don't seem to have this problem. This is why it's very important for dye sets to be properly matched. Additionally, if a swellable polymer ink reception coating on the paper is used, the individual dye droplets will be kept separated. Also, atmospheric contaminents can cause dyes to prematurely fade. (remember the epson orange fade problem 20 years ago) Epson dye prints on microporous paper exposed to ozone from xerox copiers, etc, faded to an ugly orange after a just a few days of exposure. This brings us back to the type of papers used in inkjet printing. Today most of the papers have what's called "microporous" ink receptor coating.These papers dry almost instantly. That's good and bad. The bad part is, the papers are open to atmospheric conditions unless the image is protected behind sealed glass, or sprayed with a sealant. Even pigmented prints can suffer from atmospheric fade.(think ozone) This is why properly done canvas prints are printed on water resistant canvas, and then sealed with an acrylic polymer. The glossy canvas option seems like it would be more convenient, but it does not offer the fade and physical protection that a protective coating gives.
Now, getting back the the OP's original post regarding his perception that dye inks seemed to produce a better black. In the early days of pigmented ink sets, black inks were actually a blend of pigmented and dye inks! This might even be true to some extent today, I don't know for sure. Dye ink black would look better on glossy papers, and washed out on matte papers. Matte black carbon ink would look better on matte papers, and ugly on glossy papers. Another innovation that pigment ink manufactures created was "encapsulation" of the pigments with an acrylic. This was done to make the colors brighter, and also to try and keep the pigments in suspension better. Both dyes and pigments are suspensions. But pigment suspensions are much harder to maintain. This is why pigmented ink carts are dated. If they lay around unused too long, the pigment particles will settle and congeal leading to nozzel clogging and suboptimal printing results.
Now, you have more, of the "rest of the story".