The situations of the two companies are very different. Sega endured failing hardware after failing hardware after the Genesis/Mega Drive (CD, 32X, Saturn just to mention a few). Sega also experienced back to back losses from 1997 to 2003 (in comparison Sony Computer Entertainment suffered three years of losses with PS3 and Nintendo only had one year of full losses). Moreover, Sega lost almost all third party support with the Dreamcast due to early discontinuation of previous hardware and piracy, Nintendo has more less maintained the same third party support for their systems since the Nintendo 64. Also, pirating on the Dreamcast was exceptionally easy, you could pirate on the system using a regular CD without the need for a modchip; the Wii U needs an expensive modchip to simulate the disk drive (which means there can be no cheats and hacks or the ability to play eShop titles; and Nintendo can easily do a system update to block the hardware [they have easily blocked WiiKey before on Wii] and those who choose not to update their system will not get access to new games , eShop, DLC, Miiverse, and other in-game online functionality), furthermore due to the proprietary nature of the Wii U optical disks there have been no clean disk image dumps as of yet. The last nail in the Dreamcast's coffin was not bad sales (in fact if I remember correctly the console was selling quite well towards the end, though not for the right reasons [pirating!]) it was the change in Sega of Japan's management who wanted to focus on software rather than hardware (I believe there was an interview with Sega of America's former president which confirms this).
The situation with the Wii U is different from Dreamcast but I feel it is more similar to the DS & later 3DS (though less severe, as the 3DS was selling far fewer units and had far less software at launch than the Wii U) ; in fact, two years ago there were articles stating that the 3DS would be the next Virtual Boy and that Nintendo should pull out of the hardware market because it was no use trying to compete with phones, tablets, and the more powerful PS Vita, which of course did not end up being the case. The problem with the Wii U is that it had a powerful launch but it did not continue to have the software nor the clear message about what the console is in order to keep the sales momentum going (the 3DS had the same problem; people think the Wii U is just a Wii with a tablet much like they though the 3DS was a DS that displayed games in stereoscopic 3D; and much like the Wii U the 3DS did not at launch have the flow software to keep momentum going). Nintendo has to correct the Wii U issue like they did with the 3DS. Firstly, they have to have titles lined up and ready for release for the end-of-summer period right through the holidays (with a study flow of titles ready for the period after in order sustain momentum). Secondly, they have to reduce the price of the system (around $50 is reasonable) in order to give people a reason to consider purchasing this system as opposed to its {theoretically) higher priced counter parts; hardware bundles with key software would also be useful. Lastly, they have to advertise this system and let people know about the games and features available for the system, the reduced price, and why it is different from a Wii.







