There has been a huge amount of buzz about the morning news shows over the past two months, with NBC’s Katie Couric and ABC’s Charles Gibson moving from the morning to the evening news. But what there hasn’t been is a big change in ratings, which have remained relatively steady amid all the turmoil.

In fact, there may not be any major fluctuations for months to come despite the new faces arriving on NBC’s “Today” and ABC’s “Good Morning America.” For now, the morning rankings remain unchanged.

For the most recent week available, the week ended July 16, “Today” averaged 4.9 million total viewers to “Good Morning America’s” 4.3 million. The difference of 600,000 was roughly same margin that’s separated the two shows for more than eight months now.

What’s more, “Today” without Couric was down just 5 percent from its household average with Couric for the same week last year, dipping from a 4.1 to a 3.9. That’s a negligible dip in a very slow summer for TV.

While “GMA” was down a bit more, 11 percent from a 3.8 to a 3.4, that simply reflects the season-to-date losses that the program has seen. Its current average is just a tad below where it was six weeks ago, before Gibson left.

The stability may seem like a surprise. Without Couric and Gibson, who between them spent more than three decades on the morning news, you might expect viewers to be sampling new shows or abandoning old favorites.

But the reality is that it may take months for a big swing for any of the morning shows, for several reasons.

First and most important is that viewership trends for news programs generally take months and months to play out. The shows are built for stability, with very few changes in anchor or host, designed to make them habit-forming.

Andrew Tyndall, the noted news analyst and publisher of the Tyndall Report, says that it takes about nine months after a major change for news viewing to settle into normal patterns.

Thus it may not be until next spring, nine months after Meredith Vieira joins “Today,” that NBC sees a change and longer for ABC, which has not announced a replacement for Gibson.

Change also takes a long time because some of the morning success piggybacks on evenings. When NBC’s primetime crumbled and ABC’s soared in fall 2004, that was not reflected in the morning news ratings until May 2005, when ABC came within 40,000 viewers of its rival one week. “Today” has since rebuilt its lead, in part thanks to a boost from NBC’s Winter Olympics coverage.

Finally, morning viewers are creatures of habit. They won’t make a change unless they find something truly distasteful. At this point, despite Gibson and Couric’s departures, the morning shows are essentially the same as they were three months ago: no new sets, hosts or approaches.

September will bring changes to all three morning shows, with Vieira taking up her seat, Jim Murphy joining “GMA” as senior executive producer, and CBS rumored to be mulling some morning tweaks to take advantage of Couric’s presence. That’s when ratings and the rankings may begin their slow change.

Meanwhile, in other daypart ratings for the week ended July 16:

NBC’s “Meet the Press” continued to dominate on Sunday morning, averaging 3.81 million viewers. CBS’s “Face the Nation” trailed at 2.96 million, followed by “This Week with George Stephanopolous” on ABC at 2.4 million. “Press” had its best 25-54 rating since mid-May, 

With Wimbledon and the accompanying late-night delays done, NBC's "Tonight Show with Jay Leno" took back the No. 1 spot in late night with an average 5.5 million viewers, leaving CBS's "Late Show with David Letterman" second once again with 3.6 million. ABC's "Nightline" trailed in third with 3.2 million viewers.

In daytime, CBS led in total viewers with 3.84 million in daytime dramas and 4.14 for full day, while NBC led women 18-49 with a 1.6 in both categories.

For the week ended July 21, NBC's "Nightly News with Brian Williams" finished first with 7.96 million viewers, just ahead of ABC's "World News Tonight's" 7.57 million. CBS averaged 6.9 million. NBC also nudged back ahead of ABC in adults 25-54.