The GOP did the same thing for most of the '70s and '80s; in fact, Reagan got a number of key pieces of legislation (such as his tax hike on the poor) passed precisely because the GOP voted as a block while dozens of conservative Dems could be counted on to defect from the hundreds of others in the clear majority. Remember the last time we tried to pass universal healthcare? Democratic President, Democratic House, Democratic Senate, but the Republican minority voted as a unit and enough Democrats defected to kill any legislative progress.

It's not a hard and fast rule; there are true maverick Republicans (on rare occasions John McCain has actually qualified, just not much since 2000) and there are certainly plenty of kool aid drinking Dems out there. It's not just Snowe and Collins (btw, it seems to me the latter isn't a moderate RINO who stays in the party to get elected, she's a conservative in moderate clothing who talks a good game to placate her moderate constituents) most Senators, especially long serving ones, can cruise to reelection on their record, popularity and name recognition (witness Joe Lieberman losing his partys nomination for supporting a war most of his state opposed, but being easily reelected anyway. ) Yet by and large Republicans, as at least the nominal conservative party, rally around the status quo, which makes them averse to change and independence (as well as encouraging retaliation against rebels; can you imagine a Republican version of Lieberman (to the extent Lieberman's NOT a Republican)?) That's neither good nor bad, inherently; segregation was a "tradition" in desperate need of changing, but the First Amendment is not. Conversely, the old saw that "managing liberals is like herding cats" is an axiom in liberal circles and, again, at least on paper the Democrats are the liberal party. It makes them the natural home of new political thought, but, once again, that's neither good nor bad in itself; we could as easily say that wanting to repeal the First Amendment is "bad change" as say the civil rights movement is positive change. Plus, for every Wright brother there's a hundred perpetual motion machines.

I don't really think the parliamentary system is better or worse; it has different pros and cons. It encourages, sometimes mandates, coalition governments that in turn require compromise, it allows people to vote their conscience without "throwing their vote away" (especially in countries with proportional representation and/or instant runoffs) but it's frequently slow to react in a crisis, which can often result in a very sudden and complete collapse of the government when the loyal opposition demands a vote of no confidence. Committees do nothing fast or efficiently, and it's easy to get an extreme case of "the opposite of progress is Congress" with a coup de grace thrown into drive home the point and incidentally leave the government in chaos. If you happen to live in, say, London ca. 1939 that can be a problem, but it also means you can't ram things like the IWR through the legislature. Parliamentary systems tend to have a lot more Bernie Sanderses and Liebermans, and when they align with a given ruling coalition dependent on them to retain a majority they can force some major concessions, actually accomplish things without having to get 60% of the legislature first. However, it seems rather silly to say what amounts to "there's more bipartisan compromise in a parliamentary system because the loyal opposition has no influence at all over legislation. " You get compromise, but it's not truly bipartisan; it's the ruling coalition deciding HOW conservative/liberal a given policy should be while the guys across the aisle wait to be informed along with the rest of the country what the government will do. Things are a lot MORE partisan in America these days, especially with the culture wars defining everything in stark moral absolutes that classify everyone as either a saint or devil, but in our darkest hour the minority party hasn't been reduced to taking the floor just so they can vent their spleen against the majority because they're capable of nothing else.