Overall I agree that there are far more factors than just this one of distance from the sun. As was mentioned previously, Venus is .7 AU from the sun yet is hotter than Mercury which is .38, almost half the distance from the sun. Other factors than distance are certainly to be kept in mind.
I have to disagree with the idea of Venus supporting life if it had less gravity. Venus has a number of issues preventing it from providing a nurturing environment, for example, it has almost no discernible magnetic field to protect it from cosmic radiation or solar radiation. Venus already has lower gravity than the earth at .904 g. The composition of Venus seems more of a hindrance than gravity. The axial tilt of 177.36 degrees also is strongly against it. A sizable moon such as ours, would have remedied that in all probability.
A big problem far Venus has, for a while, been posited that the lack of plate tectonics prevent the planet from being able to cool down internally. Instead of a general steady tectonic movement as on earth, Venus has periods of massive upheaval. Venus also has the slowest rotational period of any of the major planets. That would mean about 117 earth days of sunlight followed by 117 earth days of night. The temperature fluctuations would be extreme to say the least.
I do agree with the argument that mars would be better suited with more gravity, since that would enable it to maintain an atmosphere. That gives us a potential survival band of .7 AU (about 107,000,000 km) to 1.5 AU (about 227,000,000 km)
-x
Edited by EighteenDelta, : added paragraph
"Debate is an art form. It is about the winning of arguments. It is not about the discovery of truth. There are certain rules and procedures to debate that really have nothing to do with establishing fact ” which creationists have mastered. Some of those rules are: never say anything positive about your own position because it can be attacked, but chip away at what appear to be the weaknesses in your opponent's position. They are good at that. I don't think I could beat the creationists at debate. I can tie them. But in courtrooms they are terrible, because in courtrooms you cannot give speeches. In a courtroom you have to answer direct questions about the positive status of your belief. We destroyed them in Arkansas. On the second day of the two-week trial we had our victory party!"
-Stephen Jay Gould