That is a very good trailer.
As for SEGA on remakes, they actually do a fair amount. I do not know how you have forgotten games like OutRun and Golden Axe being remade a billion times over. A few years back they made one of the coolest remakes I have ever seen with Fantasy Zone II as part of the SEGA AGES 2500 series.
You again are mostly thinking of Sonic Team stuff, they do not like to work on past projects, but instead move on. This is why their concepts are always changing, usually for the worst.
Even then, what is really the point of remaking a game? Would you not rather just have a new game? Yeah, I am pretty excited for Ocarina of Time 3D myself, but that is only because I love the original and am excited that Nintendo is working on a Zelda game not based around stupid gimmicks... Besides you know, the 3D thing.
Technically it is a much more profitable and far less strenuous deal to just port games. For whatever reason, SEGA has been doing this very poorly lately, but they sell.
Look at it this way, see how much work was put into something like Super Street Fighter II HD on the XBLA and PSN? It was a big project. Almost two full years of redrawing the sprites, securing the rights to fan remixes, reworking the game to work on a widescreen plane, having to deal with hundreds of fans complaining about Guile's pants. Sure, it went on to sell like 500,000 units which was very impressive for the time, but then the fairly basic port of Marvel vs Capcom 2 comes along and completely crushes SFIIHD's reason for existing entirely.