This is not 100% correct, the only thing FICO scoring takes into affect is the % of available vs used credit. You can have $1,000,000 or $100 of available credit but as long as you use less than 10% at any given time you will see little impact to your FICO score. A manual review (ie mortgage application) might see to much of available credit as a risk, but this is usually if it is excessive (there are some people with 100's of 1000's of available revolving credit).

The other impact could be to your average age of accounts but that won't come into play until 10 years from now when the account is dropped from your credit report.

To stay on topic, Chase just did the same thing to me, but not with my MP card but a card they acquired with their purchase of WAMU. I haven't used it in about 9 months. I actually planned on closing it myself.

Many banks are looking to reduce their overall exposure.