the unfortunitely here is that the Thai law doesn't specify exactly how this works, so it leaves room for interpretation. So indeed airlines could give it their own 'flavor'. But in principle this shouldn't be different by airline of course, these aren't their rules.
Happy to read that some accept within 90 days. Stupid requirement, that no country should have. The less strict it's interpreted by anyone, the better.
not anymore, they changed the idiocy of being forced to go through agents, and they changed the name of the most idiotically named ever "visa on arrival" as well (although Thailand is also doing a great attempt for the idiocracy prize with its perfectly appropriately named visas for immigrating people).
Vietnam doesn't have visa in arrival anymore. De facto they never had it; there was a visa with the said name but unlike what it suggests, you had to apply for it in advance. They now aligned the name with the reality a few years ago, and made it so that you apply from the government directly instead of being forced to use an agent. Now, Vietnam does have visa exemption, like Thailand. But as an Australian you do not qualify.
first off, the source that you posted there is not supported by any facts. Not much of what you read there is true. There is no border run limit of one, neither has there ever been one. There used to be a limit of two, but only for land borders, it didn't apply to entries by air.
The part there that is true is that there is an effective (unofficial) limit on the time you can stay in Thailand. You might get problems entering again once you pass six months.
However, coming back to the issue of whether or not a tourist visa yields an advantage, this still isn't one. Like exemption can be refused, a tourist visa can be refused. You can even get a stamp from an Embassy warning their colleagues that you abuse the system with too many exemptions/tourist visas. The main difference between exemption and a tourist visa is knowing at an earlier stage whether or not you are deemed ok to enter. That is why immigrations officers advise entrants to have a visa next time around. That is so that they don't risk flying all the way there and then find out after that their travel history is not supportive of a new entry.
no reason to doubt, this one is quite established. If nobody publishes, announces or even talks about a tourist visa extension becoming 60 days (totaling 60 + 60), the fact that it no longer yields an advantage over exemption is still no reason to assume that it would.
A regular tourist visa extension is 30 days and you can only get one. To avoid leaving the country, you could apply for a visa in-country if you apply for one, or get the visit family extension (obviously only if you visit family).