Purchasing exclusive rights to 3rd party games are just a way to help bump up console sales, which then should help sell your other games as well. So far, Wii sales are doing well enough without needing a bump.
Purchasing the studio is to gain the IP rights and good talent. Unfortunately, the talent had better be a good fit for your company culture, or else, they leave. If you have your own talent, it might not matter as much, since they can develope the IP into the next series of that game.
Nintendo's culture is both a mixture of conservative and willing to take risks. Thus, producing a DS and a Wii, yet being cautious about how many that they produce. In a similar way, they buy the small newer companies to develope, but very unlikely to get a big existing developer, IMO.
Torturing the numbers. Hear them scream.
