The reasons I'd prefer a .tel for a directory are:
Speed-----the .tel idea is optimized with directories in mind
Ease of use-----the simple template actually makes things easier, and IMO, it fits the application it is trying to provide.
The click to call feature----as someone pointed out, .com COULD be used this way, but try it in real life, and you'll see the huge pitfalls, it simply will not work on a large global scale like .tel will.
Contact info--- With .tel your contact info is stored DIRECTLY on the DNS, the advantages of this are enormous, it makes things faster, gives you more control, and makes the data easily retrievable...
The mobile computing aspect-- This may be the biggest reason.. It will take mobile computing to a level never seen before, and this segment of the industry is growing incredibly fast right now, I don't see another TLD than can compete with these applications...
I think .tel is completely different than all other TLDs, and it may take 3-5 years to catch on, but it WILL catch on, because the applcations it provides are needed in a big way, and .tel was created with this need in mind... This isn't just your average TLD, IMO, this is something special for the future...
If I would like to build a directory site, I really dont know why I would go with .tel.