I am still trying to figure out if the 100,000 puts for $5,000 of spending is the "new" Marriott welcome offer, or just a promotional one.
Meanwhile, Starwood does have a limited time promo offer:
Regular Welcome Offer:
Earn 25,000 bonus StarpointsŪ after you use your new Card to make $3,000 in purchases within the first 3 months.
Limited Time Bonus Offer:
Earn an extra 10,000 bonus StarpointsŪ after you make an additional $2,000 in purchases within the first 6 months. This additional offer ends 4/5.
That is 35,000 Starwood points, or 105,000 Marriott points for $5,000. (Before the regular value of your spending). Looks like an even better return on your spend.