US multinationals ... can exist without [the US government] too.Yes, in the sense that they don't need to rely on the government. On the other hand, they are at the mercy of the government. One quick flourish of the pen, and a company can be destroyed. Obviously this is true at the startup scale, where a niche can simply be erased. But even at the larger scale, a national decision to back one approach can be devastating (as in FCC decisions). Or antitrust actions can decimate a company (ATT, IBM, narrowly avoided by Microsoft). The bottom line is that the government has the guns, literally.
The US Government on the other hand is absolutely and wholly dependent on large multinationals
I simply can't see how this is the case. Can you explain further? I mean, I don't see how the government needs Google or GM in any way.
power of any individual politician exceeds that of largest corporations?
I probably made that sound grander than I should have. In once sense, if every other politician is against you, then in general, winning one to your side won't help. However, in more realistic circumstances, winning a single person to your side (especially with America's committee system) can make all the difference. A single congressman influencing the language of a bill can mean hundreds of $millions in income, or the complete obsolescence of your business plan.