Why don't companies pay dividends on a graduated scale?

[ken-do-nim]

Just something I've always wondered.  When companies announce a dividend, why don't they do it something like:

"For shares held 5 years or longer, the dividend is $1.00/share.  For shares held 4 years, the dividend is $.90/share.  For shares held 3 years, the dividend is $.80/share.  For shares held 2 years, the dividend is $.70/share.  For shares held over a year, the dividend is $.60/share.  For shares held less than a year, the dividend is $.50/share."

?

That would really make people want to hold onto their older shares.