It's not the domain extension that affects your ability to use a payment provider. It's your location. If you located in the UK then Paypal, 2checkout, and Worldpay are all options available to you. There are all third party processors.
Payment gateways aren't that important as they only act as online credit card terminals for your website. It's the true merchant account that they use that are important.
To compare true merchant account with payment gateways to third party processors, read
this article. It explains it all in great detail.
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He's No Good To Me Dead
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since May 2006