It's quite simple (Score 1)

It's all about customer segregation. The normal folks who just want to stay up-to-date on the news won't pay for a subscription. Instead NYT relies on advertising with the added value of registration for better demographics. People who want to look at older articles are more likely to be professionals. They are doing research of one kind or another. They journalists, historians, politicians, and pundits. These folks are more likely to pay and it would be stupid for NYT to leave that money on the table. All of this talk about bandwidth costs and storage costs is really quite silly.