Well I'll be darned! I didn't know about the new rule...so I take back what I said...just checked the official site and here's what they say...
From section 4.12, subsection 5:
Weather, if the game is called while an inning is in progress and before it is completed, and one of the following situations prevails: (i) The visiting team has scored one or more runs to tie the score, and the home team has not scored. (ii) The visiting team has scored one or more runs to take the lead, and the home team has not tied the score or retaken the lead. (b) Such games shall be known as suspended games. No game called because of a curfew, weather, or a time limit shall be a suspended game unless it has progressed far enough to have been a regulation game under the provisions of Rule 4.10.
Full text:
http://mlb.mlb.com/NASApp/mlb/mlb/official_info/official_rules/start_end_4.jsp
Just goes to show you can't spend too much time on the Rx without learning something new!
For betting purposes, though, the books each have their own rules about it so players are wise to check it out, especially before doing a big scalp because you may end up with a loss and a push if the rules are different at the 2 books.