Time to bust out a "controversial" topic here. The Wii doesn't need a hard drive. Consoles don't need hard drives. Let me tell you why.
1. The Future. The year is 2018. You walk into your local used game store, UncleBob is furiously digging through a bin in the corner looking for a Metallic Rose DS Lite. You go up to the counter and ask to purchase Lost Winds and Boston's More than a feeling for Rock Band 360. The clerk laughs at you and says, "THERE IS NO POSSIBLE WAY TO PURCHASE THOSE ITEMS BECAUSE NO PHYSICAL COPY EXISTS." Sure, you can hope they bring the popular titles out on the virtual console for PlayStation 5, but what about obscure stuff? What about paying for the same virtual things over and over?
2. The Patch. People are predictable. They will follow the path of least resistance most of the time. The hard drive allows "updates" for games in the future they say, it solves the problem of game bugs they say. Good Intentions. Then the publisher starts breathing down their neck, whispering "Ship now, patch later" The pressure is off the programmers, the testers. They can always patch the game in a future download. NEXT THING YOU KNOW BULLY FOR THE 360 IS A BROKEN MESS CAUSE THEY LEFT THEMSELVES AN OUT. Don't believe me? Think I'm exaggerating? Look at PC Games.
3. The Bloat. The Wii has 512mb of storage. Not enough, you're running out of room, right? The PS3 has 80gig of storage! Tons more space, you'd never run out, right? WRONG. SONY FANBOYS ARE COMPLAINING THAT THEY ARE RUNNING OUT OF SPACE. No matter how much storage you give a system, the software will bloat up and fill the available space (see the path of least resistance comment above) So even if the Wii had teh mad gigabytes, we would end filling it up with 20 minute installs of Devil May Cry 4 and Pac-Man XBL goes from less than a 100k to dozens of megabytes in size.
So there we have it, a little over dramatic in places but you get the point. Now I know that fixed storage is inevitable, and sadly it's necessary. I don't have a problem with the technology itself, but the weakness of humanity means the hard drives cause more problems than they solve when it comes to game consoles.