There is certainly an attractiveness to this line of reasoning, as the SEC has several schools with outstanding football traditions. Of the 93 schools that have played I-A football for the last 35 seasons (1970-2004), the SEC has seven of the top 21 programs, if one uses average score-based (predictive) ranking as a measurement. Alabama ranks fourth over this period (behind Nebraska, Michigan, and Oklahoma), followed by #10 Florida, #12 Tennessee, #14 Georgia, #16 Auburn, #18 LSU, and #21 Arkansas. For comparison, the ACC has two top-21 programs, the Big Ten has three, and the Pac-10 and Big Twelve have four each; Notre Dame is also in the top 21. It is also worth noting that the SEC was ranked the #1 conference in the nation seven times in the 1980s, and the #2 conference two other years that decade. So for those of us who have been watching football for most of this period (as I have), it is certainly reasonable to have a belief that the SEC is hands-down the most difficult conference based on the programs' reputations.
However, with the aid of computer rankings, one can look for shorter-term trends than strengths over a third of a century. Looking instead at just the last 15 seasons (1990-2004), the SEC has only five of the nation's top 25 programs (though the #26 team is from the SEC). For comparison, the ACC, Big Ten, and Pac-10 all have four top-25 programs, and the Big Twelve has six. In other words, the five major conferences are all comparable in terms of conference strength (given that the conferences with 12 teams ought to have more top-25 programs than those with 10 or 11). During this stretch, the Pac-10 (1991-1993), Big Ten (1994-1996), Big 12 (1998-2001) have each had strong runs, but no conference has dominated the way the SEC did throughout the 1980s (or for that matter, how the Big 12's precursors dominated the 1970s).
The bottom line is that we are in a different era of college football, with conferences jostling on a yearly basis for the honor of being "nation's best". Rather than relying on teams that are consistently outstanding, what matters now is how many teams are having good seasons this year. Case in point is the Pac-10, which was the #5 conference in 2003, but the best conference in 2004. What changed was that five of the ten teams improved significantly from last year to this year (Cal and Arizona State the most; also UCLA, Stanford, and Arizona), while only two teams got significantly worse (the Washington schools). While five up and two down is hardly a statistical rarity, it was enough to move the Pac-10 from last to first given the parity among the five major conferences.
So to answer the question posed in the title, the SEC is still among the nation's top conferences. In years when the SEC's teams have more good years than bad years, this may be enough to make them the nation's best conference. However, this wasn't one of those years, and the SEC was only the fourth-toughest conference.
1 Florida State 2 Nebraska 3 Florida 4 Miami 5 Michigan 6 Tennessee 7 Ohio State 8 Kansas State 9 USC 10 Penn State 11 Virginia Tech 12 Notre Dame 13 Oklahoma 14 Texas A&M 15 Washington 16 Texas 17 Colorado 18 Alabama 19 Georgia 20 Virginia 21 Auburn 22 UCLA 23 Oregon 24 Syracuse 25 Iowa 26 LSU 27 Wisconsin 28 Arizona State 29 Texas Tech 30 Clemson 31 Michigan State 32 Georgia Tech 33 Purdue 34 California 35 North Carolina 36 Washington State 37 West Virginia 38 North Carolina State 39 Utah 40 BYU 41 Arkansas 42 Stanford 43 Arizona 44 Southern Miss 45 Mississippi 46 Boston College 47 Colorado State 48 Air Force 49 Louisville 50 Fresno State 51 South Carolina 52 Mississippi State 53 Illinois 54 Minnesota 55 Miami (Ohio) 56 Oregon State 57 Oklahoma State 58 Maryland 59 San Diego State 60 Toledo 61 Kansas 62 Missouri 63 TCU 64 Indiana 65 Pitt 66 East Carolina 67 Memphis 68 Northwestern 69 Bowling Green 70 Kentucky 71 Iowa State 72 Wyoming 73 New Mexico 74 Cincinnati 75 Rice 76 Wake Forest 77 Baylor 78 Western Michigan 79 Louisiana Tech 80 Hawaii 81 Houston 82 Vanderbilt 83 Duke 84 Tulane 85 Utah State 86 Navy 87 San Jose State 88 Tulsa 89 Rutgers 90 Northern Illinois 91 Ball State 92 Central Michigan 93 Army 94 UNLV 95 SMU 96 Temple 97 Ohio 98 Akron 99 UTEP 100 New Mexico State 101 Louisiana-Lafayette 102 Eastern Michigan 103 Kent State 104 Arkansas State
Note: if you use any of the facts, equations, or mathematical principles introduced here, you must give me credit.