MSNBC correctly notes that it's not as momentous as Specter's switch, since Griffith has been voting with the Republicans on many/most major issues anyway.
However, like Specter's move (and unlike, say, Jim Jeffords' move several years earlier, which was fully ideological) it is based almost entirely on his desire to get re-elected. In fact, it may be even more so than it was for Specter.
After all, when Specter first got elected to the Senate as a Republican back in 1980 as part of a massive influx of new Republicans that allowed them to win control of the Senate, he was hardly the only moderate Republican. Lowell Weicker (later ditched the party and served as Independent Governor of Connecticut), Charles Percy, Nancy Kassebaum, Bill Cohen, Charles Mathias, David Durenberger, John Danforth, Warren Rudman, Mark Andrews, Mark Hatfield, Bob Packwood, John Heinz, John Chafee and Bob Stafford were all very moderate Republicans, and perhaps Ted Stevens, Bill Roth, Rudy Boschwitz and Al D'Amato (and maybe even Bob Dole). This year, it was Arlen, the two ladies from Maine, and then after them, next would be Dick Lugar, who probably wasn't even in the top half when it came to moderate Republicans back then.
On the other hand, even though the Democratic house majority was only slightly smaller (244-191), the majority in the Northeast was much, much smaller, 65 out of 113, 57.5% (as opposed to 76 out of 92 today 82.6%)
Outside of the northeast, the majority was actually larger (55.6%) in the 97th Congress than today (52.8%). This was of course due to the difference in the South, where the voters hadn't made the big switch yet. In the greater South (defined as the 11 Confederate states plus Oklahoma and Kentucky), in the 97th Congress, Dems had 79/121 (65.3%) of the seats; today they have 61./142 (43.0%). The difference is even more dramatic if you leave out the border states of Arkansas, Virginia and North Carolina (which all have a larger percentages of Democrats in their delegations today than in the 97th Congress). 69/96 (71.9%) in the 97th Congress. 44/114 (38.6%) today.
Anyway, outside of the greater South and the Northeast, in the 97th Congress, Dems had 100 of 201 (49.8%), just shy of the majority, while today, they have 120/201 (59.7%). This is, of course, mostly due to the significant Democratic gains in the West