There seems to be some confusion about two very different things;
proof of funds when getting a visa from a thai consulate (at the consulates which require it)
AND
proof of funds when entering the country (if you are unlucky enough to be asked by passport control when you stamp in).
At the consulates which require proof of funds to issue tourist visas you CANNOT use cash, you must show a bank statement, but it doesn't have to be a thai bank account.
If you are asked to show proof of funds when you stamp into the country you CANNOT use a bank statement, you must show cash, but it doesn't have to be thai baht, it can be in any currency.
Just wanted to touch on those things because they come up quite often in topics.