Madson is starting the season on the DL and likely won't be allowed to pitch back to back games til July at the earliest after the TJ surgery. If Frieri pitches anywhere close to how he did last season Madson won't be able to win the job. And there really isn't a point to giving Madson the job that late in the season when he's only on a one year deal.
While Ichiro isn't anywhere close to what he used to be, he did hit .322 with 14 SB in only 67 games after the trade to NY. With all the injuries he's going to see a lot of playing time and I think it's reasonable to expect him to hit .290 with 25+ SB. Not great, but I think it's more likely you drop Madson in the first half of the year than it is he finishes with 20+ saves.