Buddhism in context, differences through SE Asia? What are some specific cultural aspects of different countries in SE Asia that are integrated into Buddhism, but that might not actually be consider purely Buddhism?  

In other words, comparatively, why is Buddhism in Thailand different than Buddhism in Cambodia.  And what would the main differences be?
Burma is the only one in the world that still have buddhist ancient learning system (mukkhapāṭha). The strongest buddhism country is Burma. The tipitaka-strictest nikāya is Shwegyin Nikaya of Burma.

About a hundred year ago, in colonization war, thailand began to lost our tipitaka memorizing system. We need to get western's learning culture to protect our land from colonial possession. The central region of Siam reform memorizing learning system to academic learning system. Mun's students (Phun acaro, etc) were the last tipitaka memorizers of thailand.

Mun was the north-eastern region of thailand, that got reform order from the central region. And Lao was the north-eastern colony of thailand at that time. So Lao tipitaka memorizing learning system had began to lost since that time, too. Kambodia, also.

Nowadays, Lao and Kambodia monks equal to thai mahanikaya tradition. They are not forest tradition.

Thailand and srilanka have lost tipitaka learning system in colonization war.

Thailand began to lost our tipitaka learning system about 1855 and after that years (Bowring Treaty).

The king trying to protect thailand by changing every rules of us. They also changed learning system of monk, too. They cancle memorized learning system, then took a writing learning system instead. We also started to lose abhidhamma learning system  at this time, too.

Writing learning system is for kamaguna 5. They save memorizing times to consume kamaguna 5.

Arahanta haven't writen. They keep tipitaka in their mind.

Before that time we still having tipitakathara, such as mun bhuritutto (he not memorized enough to be bhikkhu-parisūpaṭṭhāpaka). But after the changing, we never have tipitakathara anymore. The elder tipitakathara died. Never have any newer to be instead of them.

So, thailand loose our tipitaka learning system so long time ago in colonization war.

Buddhadasa was a monk after we lost tipitaka learning system. He is tipitaka cutter.