A lot of people think so and that makes it so when they bid more. Check to see which are parked, which are developed, and which are for sale (and the offering price), etc.
Possibly, in particular when you own the .com.
Holders of alternate extensions are obvious, possible buyers.
Plus, when the other extensions are developed there can be some traffic leak to the .com.
Its also a scarcity issue. Lets say a company wants a particular keyword domain name (.com) but the owner wants 10k for it. They look to see other TLD's are taken. If they are, it would make it difficult for them to just register another gTLD - more than likely coming back to you.
The simple, and generally correct answer, is yes. If all tld's are taken, then some assessment of value or potential value has already been concluded by the registrant(s) of those tld's.
If the domain is a .com yes definitely; except in the case where all the other tld's belong to the sam eperson. Then it might be that a company got all other names to protect their identity and the ,com was already registered when they did that.
I occasionally do this myself as a domainer. If I *really* like the keywords, I buy the major extensions with the .com. I can then offer it worry free to the buyer as a package. The bundles seem to have helped me get listings and sales at Moniker auctions too. Don't go overboard with this strategy though since it increases prices significantly.
With some domains I deliberately leave the .net and others on the registry floor to encourage buyers to grab the minor extension and then want my .com. In particular I do this with IDN most of the time to encourage real development in IDN by end users...
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(Just another mathematician obsessed with proving P != NP -- that is a math joke for job security)
Smile! In a few short years you will realize that these are the good old days!
Check if the other extensions are developed though... often they are just parked.
So the fact that other TLDs are taken is not always an indication that the name is really good.
