No, and no. Your economics is wrong. Mandated healthcare would theoretically be cheaper as the responsibility is shared across the board. The amount of money needed to fund healthcare in America will remain relatively static, the only difference being that under the plan proposed by Senator Obama, less people would have to pay more money in order to balance things (in particular parents, as there will be a mandate on children). It has nothing to do with supply and demand. Health insurance claims would not suddenly increase, and the amount of funds flowing into the system would be virtually the same under both plans - if not with a slight advantage to Senator Clinton due to the higher subsidies and the arguable fact that a shared burden scheme would overall draw more money.
Of course there will be stupid people who will refuse to pay mandated healthcare or who elude the controls put in place, until they or a family member or friend get cancer or something so people who have been doing the right thing all along and paying their health insurance would end up subsidizing them. The truth is nobody wants to pay money to help other people unless of course, they end up needing assistance themselves in which case they transform into the most avid socialist. This is a reality for both plans, only under Senator Clinton's such a freedom to mooch is discouraged as those who do not pay will have their wages garnished (with reasonable measure).
I'm not familiar with the Massachusetts system, but I doubt it is an ideal model. Mandates on universal healthcare have functioned well in European countries far longer than anything introduced in the state of Massachusetts (2005-2006?), so pardon me if I'm not compelled by this parallel. I will however point out that Senator Clinton's plan aims to provide a refundable tax credit should the cost of premiums exceed a certain percentage of one's income (estimated at 5%-10%).
Cost control measure proposed by both candidates are equally extensive, so I am unsure where this conclusion that Senator Obama holds dominance originates from. I won't revisit the idea which ICO cites concerning Medicare again because I have already expressed that; a. I don't think it's financially sustainable and b. No current candidate is proposing such a plan. Furthermore, I'm not at liberty to declare what congress will or will not pass as I am not a member of congress and I have been surprised by what has slipped through before. I will however note that to speculate Senator Obama's plan or any proposed expansion of Medicare would somehow receive a less tepid treatment than an individual mandate would be stretching the imagination a little.
The comparison to car insurance is just nonsensical. The number of people not paying car insurance would be astronomically higher if it were not mandatory. Senator Obama drew the same analogy and I will ask you what Paul Krugman asked of him - What's your point? Are you saying states shouldn't require drivers to have insurance? Are you saying that more people would be covered if only those who wanted to purchase car insurance did so?
The fact still remains that 
on paper (which is where all these health plans we're discussing are currently situated) Senator Obama's Healthcare plan 
relies on people not wanting or needing health insurance in order to remain sustainable and so it isn't universal. It is a step away from what Democrats would like to see from Universal Healthcare. That is what I said in my first post and it hasn't been effectively challenged. You and IC can say "oh but I like his plan better" or "we should expand Medicare", however it doesn't change the fact.