"Tiger" is a perfectly fine trademark
Systemax, Tiger Direct's parent, only claims to own the term "Tiger" for use on the following goods and services:
Mail order catalog services featuring computers and computer related products; and Retail store services featuring computers and computer related products.
They don't claim to own the word "tiger," they claim to own the word "tiger" when it is used to designate the source of certain products or services. That is, they own the goodwill they've developed in the term "tiger" to the extent that consumers associate that word with the source of certain goods or services sold under that term.
With a trademark, you don't own the mark in gross, you own the mark in relation to the trade for the goods or services that you use the mark on. So, Apple Computer owns APPLE for selling computer hardware and software (along with a lot of other stuff, of course). However, Apple Corps Limited, the Beatles' recording company, has a registration for the term "Apple" for:
gramophone records featuring music; pre-recorded audio tape cassettes featuring music; audio compact discs featuring music; pre-recorded video tape cassettes featuring music; [ video laser discs featuring music ]
The touchstone is always the consumer. As soon as consumers no longer associate a trademark with a particular source of products, then the term is no longer functioning as a trademark.
This is why Tiger Direct is concerned about OS X Tiger - if consumers only come to associate "Tiger" for selling computers with Apple Computer, then Tiger Direct has lost its mark.