Identical TM in different countries?

[bluemeteor]

Say a US company launch a site: xreview.com. But they don’t register tm or company in other countries.
There many countries only admit registried tm. So can ppl in one of this countries launch a same site also call: xreview.net and review the same industry?

A live example is this, seoking.com is owned by a company. While seoking.net & seokings.com are owned by another company.