Even though "I" fares are in Business Class, they are essentially the "LUT" version of Business Class fares, hence the restrictions and penalties for changes can be severe (and often more so than say M or B fares, which are considered the 'top end' of the Economy fares).

As hfly correctly pointed out, "I" fares vary greatly by market for advance purchase/min/max restrictions. The Eastern European destinations usually have the most reasonable "I" fares with the least number of restrictions...