The vidgame biz has caught sequelitis.

Nintendo and Sony will rely mostly on new installments of proven franchises rather than launching new properties to drive their videogame businesses through the end of next year.

Much attention was lavished on the next renditions of Nintendo’s “Super Mario Bros.,” “Super Mario Galaxy” and “Metroid” and Sony’s “Final Fantasy,” “Metal Gear Solid,” “God of War” and “Gran Turismo” during the Tuesday tubthumping by those companies in connection with the Electronic Entertainment Expo taking place in downtown L.A. this week.

The emphasis on squeezing more sales out of existing franchises is also hitting the hardware front, with Sony gearing up to bow a new version of its PlayStation Portable handheld as a pure digital entertainment device.

The PSP Go targets consumers who want a device that can store games, movies, TV shows, music and other content instead of having to carry CDs, DVDs and game discs when they travel.

“We call it the worst-kept secret of E3,” said Jack Tretton, prexy-CEO of Sony Computer Entertainment, while unveiling the PSP Go at the Sony’s newser, which packed 5,000 attendees inside the Shrine Auditorium. “Given this industry’s inability to keep secrets, we are an industry leader. We won’t be outdone by anyone.”

The $249 device, which will hit retailers in October, is 50% slimmer than the current PSP, which will still be sold. That device has sold 50 million units since 2005; 15 million PSPs were sold last year.

The PSP Go should help Sony compete more aggressively with Apple as it features a far larger screen than the iPod and can act as both a small videogame console and video player.

Sony plans to make many of its major franchises — including “Gran Turismo,” “Resident Evil,” “Metal Gear Solid” and “Little Big Planet” — playable on the PSP this year.

The reliance on franchises is a safe strategy that should prove profitable for the companies considering previous versions of the games were bestsellers when they were released.

Nintendo also continues to dominate in the casual games category with its Wii.

While nearly 300 million people are actively playing games in North America, Japan and Europe, another 150 million have considered playing games, according to a survey conducted by Nintendo. It’s an audience the company and its rivals are clearly starting to go after with games that don’t require hours of commitment and get other individuals involved.

The Wii version of “Super Mario Bros.,” for example, will enable four people to play at one time.

“No one was born an expert gamer, but everyone was a new player at one time,” said Nintendo prexy Satoru Iwata, who added that “Mario Kart” for the Wii and the console’s Wii Wheel helped lure new gamers.

A new version of the company’s Wii Fit will also hit store shelves later in the year; the first version has been a major crossover device for the games biz.

Sony is trying to boost consumer interest in its PlayStation 3 with a lineup of exclusive titles, including actioner “Uncharted 2”; racer “Gran Turismo 5”; spy game “Agent,” from Rockstar Games; and a massively multiplayer online version of “Final Fantasy,” the series’ 14th version.

Company said 35 exclusive games are planned to roll out for the PS3 this year. It hopes to sell 13 million of the $400 consoles this year.

It had always intended to have more games, but publishers opted to collect more coin for their games by making them available on systems from Nintendo and Microsoft as well.

The tones of the two press conference were markedly different, as is usually the case, with Nintendo heavily focused on family fare, while Sony hits hardcore gamers with more violent titles.

But Nintendo still had some edgier fare to show off, such as an exclusive version of the horror sci-fi game “Dead Space: Extraction” and “Metroid: Other M.”

Sony is also hoping to boost interest in its PS3 by adding more content to its PlayStation Network, which competes with Xbox Live and houses the company’s digital downloading service.

PSN has grown to 24 million members — 11 million in North America. PSN’s digital video service, which launched with movies, TV shows and other Web content last summer, has added Disney, Nickelodeon, Starz, G4, E!, HDNet and Magnolia Films as content providers and will now also be available on the PSP.

And PlayStation Home, an online social networking service, has attracted 6.5 million users worldwide since launching last year.