[quote name='rickonker']Sega still exists; they just decided not to make any more consoles.[/quote]
Woah woah, hold on now.
SEGA didn't just decide to call it quits out of the blue. SEGA had to stop making consoles. It was leading them close to bankruptcy as not only were their past mistakes catching up to them, but it also ended up causing a huge loss in sales for the Dreamcast.
Dreamcast was meant to destroy the N64 and PlayStation to make up for the failure of the Saturn outside of Japan. Because of the failure of the Saturn, people aren't sure they want to invest in the Dreamcast after they've been burned by the company who told them CDs were the next thing (SEGA CD) and then released another add-on that went right back to cartridges (32X) and then abandoned that as soon as their next big console came out, which supported CDs (Saturn). Then comes the PS2 and SEGA's losing even more sales.
It got to a point where they were so back up on unsold consoles, they had to stop at some point because their warehouses were practically filled. SEGA ended up losing to the PS2 and all of their past mistakes catching up to them. They originally planned to file for bankruptcy but in turn then decided to become a third party company.
Prior to their merge with Sammy, they were actually making more money as a third party developer than they were as a hardware company.
While many people say the same could happen to Sony the same way things happened with SEGA, it could never actually happen for one reason alone: Sony doesn't soley make video game hardware. They have enough money from other things to keep them afloat. SEGA didn't.