What I liked about the Ending (Spoilers)
Whether it was intended or not, I have decided to interpret the ending this way...
Just because Doug went back home doesnt mean he gave up on her. I think by leaving the money and the luggage for her was a gesture saying, "Hey, you know I still care even though you're nobody's little girl."
The wife was right when she said, "She's not Emily." Doug knew it, and so did Allison.
But, in an odd sort of way, when Doug told the neighbor that "she has my number"...it was like parents giving their daughter the space she needs to figure stuff out on her own, but giving her the knowledge that she could come home anytime she likes.
In fact, when we see Allison in the bus station on the phone with Doug, she is dressed and groomed properly. Even though she tells Doug she is going to Vegas, a part of me wants to think that she is actually getting on the bus to "go home".
I think her call to Doug was just a way of evaluating if Doug really still wanted her in his life. She figured out that he and his wife did, so she heads towards the bus taking her Indianapolis.
Looking at the ending in this light, I liked it very much.