I hate to leave off the night with topics like the previous one, so let's get back to some Torah. The Sha'agas Arye (#87) asks the same question we raised here in slightly different form. The Chachamim dismiss R' Yehudah's requirement that chameitz be disposed of by burning (Pesachim 27) by arguing that such a stringency leads inevitably to a leniency -- if one has chameitz but not firewood, one cannot fulfill the mitzvah of disposing of chameitz.
Recall that according to the last mishna in Temurah the ashes of issurei hana'ah which must be burned may be used, but the ashes of issurei hana'ah which can be disposed of in any way may not be used if these items are burned.
If chameitz comforms to the same rule, then why should the Chachamim draw attention to a potential leniency caused by a lack of firewood when there is a a far more glaring leniency inherent in R' Yehudah's opinion -- according to R' Yehudah who demands that chameitz be burned the ashes of chameitz would be permitted while according to the Chachamim these ashes would be prohibited.
Since the gemara does not raise this possibility it suggests that even the Chachamim would permit the ashes of burned chameitz -- but why is chameitz different than other issurei hana'ah?