No...it's not really a smaller brother, but rather a segmentation of the product lines into business versus consumer so rather than i5 is to i7 what Celeron was for Pentium, but it will be more like i5 is to i7 what Pentium is to Xeon.
I guess you do have a point..
Xeon seems to be more server related, which is a whole other segment, but i7 (high performance) would be mainly for desktop as would i5 (mainstream), so the celeron/pentium compare doesn't seem so far fetched.
It would be somewhat logical for i7 to have a smaller brother similar to celeron.