Symbology on standard terminal arrival (STAR) charts: T-ended vs arrow-ended lines?
According to the FAA Chart User's Guide, the arrows are transition routes and the 'T' is "Altitude change at other than Radio Aids." So your original assumption is correct.  

Regarding DSERT TWO ARRIVAL and BUSTD. You are correct that the altitude doesn't change at BUSTD when proceeding to YOLOW, but it does change (9000 to 8000) when proceeding to BAYTA. That is why there is a 'T' at BUSTD.