America's 70-year love affair with traditional TV is growing stronger despite the video explosion on the Internet and mobile phones, according to a Nielsen report released on Tuesday.

The Nielsen report, which is the media research firm’s first direct comparison of video entertainment’s “three screens”: TV, PC, and mobile phones, offered counterintuitive results.

Americans spend 133 hours per month watching TV or time-shifted TV, while they spend just 26 hours per month on the Internet. Americans spend about two hours per month watching Internet video, and about three hours watching mobile video.

The time spent watching TV rose four percent from 2007 while Internet surfing saw a nine percent gain from last year.

The report shows that traditional TV is thriving, and that talk of the demise of the 30-second spot ad, and TV being replaced by a larger video sector may be premature.

“TV remains far and away the most popular form of video entertainment and it is definitely holding steady,” said Gary Holmes, a spokesman for Nielsen. “Clients have been clamoring for us to develop a common metric across all three screens so they can get a sense of scale and proportion among the three.”

There is a lot at stake for all three forms of video media.

Expenditure on TV and Internet advertising, which amounted to about $90 billion in 2007, could take a hit after 2008 because of the slowing U.S. economy, and eMarketer expects TV to take the brunt of that hit.

“U.S. TV advertising spending is likely to grow in 2008 on the back of the presidential election and the summer Olympics,” Ben Macklin, eMarketer’s senior analyst, wrote in a report. “But in 2009 and beyond the traditional TV advertising environment will become increasingly challenging.”

The research firm expects TV ad spending to grow just 2.1 percent year-over-year from $67.8 billion in 2007 to $75.4 billion in 2012, while online ad spending is expected to grow 19.2 percent for the same period from $21.2 billion to $51 billion.

Ad spending on mobile phones is still very small.

Americans over 35 watch more TV than those under-35, but older Americans spend up to three times as much time on the Internet as the younger brackets, the report found.

The heaviest web users are between 35 and 64.

Women tend to view video content on Internet sites affiliated with TV, while men tend to watch more consumer generated video content on sites such as YouTube and MySpace.