This (lack of) brake issue is a serious one. I (and others) have brought it up at various times in the past. At the PT level, it is not a technical issue, but rather a cost issue.
All models from the 1445 and above do have either internal wet spring-applied/hyd pressure release or external dry Brake Tender that basicaly operates in a fail-safe manner.
In my opinion, they should equip all the smaller models with the internal wet brakes (or at the very least, offer it as an option) for the very reasons you and others have mentioned.
As I was looking specifically for a machine suited for work on very steep terrain, brakes were a primary consideration, and the Brake Tender system on the 1845 works well indeed.
A good hyd shop can replace the wheel motors ( all or at least 2) on the other models with ones with integral wet disk brakes, but it will not be cheap. On the other hand, it would be only a nominal cost at the factory level to equip them this way or offer it as an option.
I fully agree that this is a serious safety issue, and one that PT has chosen to ignore due to cost considerations. How to get them to change, I do not know. This issue has been raised numerous times before to no avail. Hopefully it won't take a serious injury or death to wake them up.
Talk to a good hydraulic shop for an estimate on upgrading your particular unit. It should not be hard to do, but may involve some modification or customization. It also may widen the wheel track somewhat, which could be a problem for some or a boon to others due to increased side-hill stability.
Good Luck whatever you do...
Rip